While Australia and New Zealand battles record-smashing heat, interminable drought and deadly bushfires, the United States is in the grip of a polar vortex, with temperatures plunging to their lowest in history.

After Adelaide's mercury soared to an unprecedented 46.6C last week, toppling a heat record from 1939, seven people have died in freezing temperatures and heavy snow across America's Midwest.

A nine-year-old died in a crash on the icy roads and a 75-year-old man was hit by a snow plough as authorities warned of the danger of "instant frostbite", with Chicago set to be colder than Antarctica, Alaska and the North Pole tonight.

New Zealand is sweltering in record-breaking heat while the United States is suffering a polar vortex.
New Zealand is sweltering in record-breaking heat while the United States is suffering a polar vortex.

Schools, offices and colleges were closed across the region with temperatures on the city's Lake Michigan plunging to an icy -29C on Wednesday local time, and set to break its -32C record early on Thursday.

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Niwa said Thursday would be the "peak" of the heat wave in New Zealand, and predicted temperatures could reach 37C in parts of north Canterbury.

Australians and New Zealanders, of course, have the opposite problem as power failures have been causing misery with air-conditioned use on the rise.

Twelve bushfire warnings are in place in Austalia for the state and the Huon Highway that connects Hobart to southern Tasmania is partially closed.

Train services in Wellington crashed on Tuesday evening following record-high temperatures which shut down the network.

Frost covers part of the face of University of Minnesota student Daniel Dylla during a morning jog along Mississippi River Parkway. Photo / AP
Frost covers part of the face of University of Minnesota student Daniel Dylla during a morning jog along Mississippi River Parkway. Photo / AP

In the US, blizzard-like conditions across the Midwest saw 1000 flights cancelled in the Chicago area alone, the postal service cancelling its operations, and rail tracks set alight to keep trains moving.

Snow plough drivers in Wisconsin were struggling to deal with record snowfall, with Sturgeon Bay blanketed under 32.5cm — more than double its 1949 record — and Manitowoc seeing a 26.7cm snowfall, breaking a 1918 record of 18cm.

There is worse to come, with a blast of Arctic wind racing through Maryland on Wednesday and Baltimore City Health Commissioner Mary Beth Haller calling the temperatures "dangerously cold".

Wind chill in northern Illinois could fall to a -48C, which the US National Weather Service called potentially "life threatening", advising people not to drive or even leave their homes unless necessary.

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A person walks along the lakeshore, Wednesday, Jan. 30, 2019, in Chicago. Photo / AP
A person walks along the lakeshore, Wednesday, Jan. 30, 2019, in Chicago. Photo / AP
A warning sign is covered by ice at Clark Square park in Evanston. Photo / AP
A warning sign is covered by ice at Clark Square park in Evanston. Photo / AP

Weather Prediction Center meteorologist Brian Hurley said Minnesota temperatures could hit -34C with a wind chill of -51C. "That's quite dangerous," he said. "You're talking about frostbite and hypothermia issues very quickly, like in a matter of minutes, maybe seconds."

Donald Trump caused controversy when he seized the opportunity to question how climate change could really be warming the planet if the weather was so abnormally cold. "What the hell is going on with global warming?" he joked. "Please come back fast!"

The backlash was instant, with Americans demanding how their President — who controversially pulled out of the Paris accord to reduce emissions in 2017 — could deny the widespread scientific consensus.

But experts explained that the chilly conditions were a result of the same problem, with the warming Arctic triggering changes in the jet stream and pushing polar air down to lower latitudes than usual, including the Midwest and Northeast of the US.

The nation is looking to Australia to provide context for its big freeze, with the New York Times reporting on the extreme heat, bushfires, business closures and power shortages gripping the country. Australia's drought "has gone on so long that a child in kindergarten will hardly have seen rain in her lifetime", wrote the newspaper, noting that the temperature in New Zealand had also broken heat records.

"Warming centres" for homeless people have opened in the bitterly cold American Midwest, with buses driving the streets in the hope of preventing more deaths as the big freeze sets in. It comes just months after California was ravaged by its most destructive wildfires.

And the problem is global, of course. The past four years have been the hottest on record, according to the World Meteorological Organisation, and ocean temperatures have broken records for several straight years.

Extreme heat and drought is devastating the health and livelihoods of tens of millions of people, especially in South Asia, and destroying crops.

A PLOS Medicine study projected a fivefold rise in heat-related deaths for the US by 2080 and 12 times more in the Philippines.

MAP REVEALS GLOBAL PROBLEM

It's unusually cold in parts of the US, but global temperatures are still warmer on average.

One map proves that Trump is wrong and that global temperatures are on the rise.

Analysis from the University of Maine's Climate Change Institute shows the world on January 29 was 0.3C warmer on average compared to the baseline, Vox reported.

Worryingly, these extreme weather events could be becoming increasingly common.

Recent research shows that the frequency of winter polar-vortex events has increased over the past four decades, perhaps because of climate change, Business Insider reported.

Temperatures are rising fast twice as fast in the Artic as the rest of the planet, which means there is less disparity in temperature between the North Pole and continents at lower latitudes.

That is affecting air pressure levels which weakens the jet stream.

A University of Maine Climate Change Institute map showing how different global temperatures were compared to a baseline from 1979 to 2000 - around the whole world.
A University of Maine Climate Change Institute map showing how different global temperatures were compared to a baseline from 1979 to 2000 - around the whole world.

A meandering jet stream can disrupt the natural flow of the polar vortex, leading to what we see today.

The US is looking to Australia to provide context for its big freeze, with the New York Times reporting on the extreme heat, bushfires, business closures and power shortages gripping the country. Australia's drought "has gone on so long that a child in kindergarten will hardly have seen rain in her lifetime", wrote the newspaper, noting that temperate New Zealand had also broken heat records.

"Warming centres" for homeless people have opened in the bitterly cold American Midwest, with buses driving the streets in the hope of preventing more deaths as the big freeze sets in. It comes just months after California was ravaged by its most destructive wildfires.

And the problem is global, of course. The past four years have been the hottest on record, according to the World Meteorological Organisation, and ocean temperatures have broken records for several straight years.

Extreme heat and drought is devastating the health and livelihoods of tens of millions of people, especially in South Asia, and destroying crops.

A PLOS Medicine study projected a fivefold rise in heat-related deaths for the US by 2080 and 12 times more in the Philippines.

RECORD HEAT HITS NZ

Temperatures in the South Island were cranked to the max yesterday, with Cheviot reaching 36.1C - New Zealand's warmest temperature this summer, Pukaki (Mt Cook) reached 34.8C, Hurunui 34.4C and Masterton got to 32.7C.

Fine weather is on the cards for the Auckland region again today with a high of 27C, although there will be some cloud in the morning and evening, with easterly breezes.

MetService meteorologist Hannah Moes said today's top main centres were forecast to be Blenheim in the South Island on 34C, and Masterton in the North Island on 33C. But many more spots were tipped to top 30C, a trend the country has experienced since the heat began on Sunday.

"Today is looking very similar to the past few days, apart from some cloud in the morning and at night it is looking fine for most places," Moes said.

The country's eastern centres were looking to be the pick of the bunch again, with high temperatures boosted by the foehn effect as the air mass passed over the country's central mountain ranges.

The exceptions to the fine weather were gale northerlies forecast about Fiordland and strengthening westerlies in central New Zealand.

Last night was another sweltering one for Auckland, with the mercury hovering around 20C before dipping to 18C about 6am.

MetService meteorologist Lisa Murray said some respite from the heat was coming for parts of the country in the form of a punchy southern system.

"We are still under this ridge of high pressure, what we are seeing is a slight increase in winds," she told the Herald.

"We've been seeing these sea breezes in the afternoons cooling things down, sometimes by as much as 10 degrees.

"What we're going to see now is as the new front approaches the winds will pick up over Fiordland and other places gradually and then across the country."

The front is expected to slide northeast across the South Island and the lower North Island which will bring gale-force winds to many areas tomorrow.

But the run of warm weather isn't over, another ridge of high pressure is expected to arrive over the country on Saturday and Sunday.

Since the start of the week, there have been at least three cases of children being locked in vehicles in sweltering conditions.

Police advised members of the public who see children in distress to contact emergency services immediately.

St John ambulance crews have also been kept on their toes during the week with a number of heat-related incidents since Saturday.

Assistant director of operations for St John Tony Devanney advised people to be careful in the hot weather by avoiding the sun as much as possible.

"Those with existing health conditions and illnesses also need to take special care," he said.

Meanwhile, train services in Wellington crashed on Tuesday evening following record-high temperatures which shut down the network.

About 8000 commuters had to find another way home after the outage affected the Hutt and Johnsonville lines.

Temperatures in the city passed 30C around 4pm, including a record-high 30.3C in Kelburn.

Elsewhere, Auckland Zoo residents Burma and Anjalee, two Asian elephants, were treated to wheelie-bin sized ice blocks to cool them down.

According to Watercare, Auckland residents drank or used 524 million litres of water on Tuesday which is 20 million litres more than the previous record.

"As the mercury rose, so did consumption," it said in a statement.

"Watercare worked to supply more treated water, so that no taps ran dry: producing 530 million litres ―six million litres ahead of demand."

- additional reporting by AP, NZ Herald