Hundred-year-old records are tumbling as unrelenting heat sets New Zealand on course for its hottest February ever.

Most regions are between 2C and 3C hotter than normal as the strongest La Nina weather pattern in 30 years drives warm air and heavy humidity over the North Island.

"We are only halfway, so it could yet change. But for the first two weeks we've run at our hottest ever," said climate scientist Georgina Griffiths, of the National Institute of Water and Atmospheric Research. "And February is usually our hottest month.

"Even if we got extremely cold for the rest of the month, it's not going to be a normal February."

While some regions have missed out - Otago has had only five dry days in the past 30 - most are basking. Some east coast regions, such as Gisborne, Wairoa and Hawkes Bay, are a staggering 3.9C warmer than their mean temperature for the month.

Auckland has consistently reached 27C, and with humidity exceeding 70 per cent, it has felt a few degrees higher than the thermometer reading.

Weatherwatch analyst Philip Duncan said: "Many people say the heat is worse here than Australia. The highs don't sound as dramatic, but as soon as you start walking, in 26 degrees and humidity, it is just exhausting.

"There's no end in sight. We are having an Indian summer in the North Island this year."

Forecasters expect the warm weather to continue, but not with the extreme highs of the last two weeks.

Piha lifeguard Tony Johnston said that after a quiet Christmas, hordes of people had visited west coast beaches in the past two weeks to cool off.

"It's been super hot, perhaps muggier than usual. We've been rotating the water patrols more than usual so everyone can get a dip more often."

Mr Johnston said that while resources had been stretched in the surf at times, most first-aid help had been given to people hurt on land. "Quite a few people have burned their feet on the black sand."

MetService weather ambassador Bob McDavitt said the rest of February would be "warm, but not brilliantly warm. Summer peaked in early February, and temperatures have already begun falling."

Mr McDavitt said the key contributor to the warm weather had been the lack of southerly winds. He said our warm air was sourced from Australia and the Pacific Islands, driven by La Nina's northwesterly winds.

Three townships have registered all-time records this month.

The MetService weather station at Timaru Airport reached 40.3C on Waitangi Day when an Australian heatwave crossed the Tasman Sea.

But yesterday, Niwa revealed that its garden-based weather station in Timaru, which is more sheltered, reached 41.3C. That reading is by far the highest in the South Canterbury town's 125 years of records, and only 1.1C shy of NZ's hottest-ever day, in 1973 in Rangiora and Marlborough.

Also on Waitangi Day, the temperature in Te Puke hit 31.2C.

On February 2, Gisborne had its warmest day in 105 years of record-keeping when the mercury climbed to 36.3C.

Much of that heat was generated by a phenomenon known as the foehn effect, when the wind heats up dramatically as it drops down a slope, shedding its moisture. As it travelled eastward, between Taranaki and Gisborne, it dropped out of the mountain ranges of the central North Island and the temperature rocketed more than 15C.

The conditions observed in February are typical of a La Nina weather cycle, bringing warm and wet weather to the North Island and dry hot weather to the South Island. Meteorologists have indicated this is the strongest such cycle since 1973.

La Nina has also encouraged unwanted phenomenons. Its warm currents were responsible for bridge-breaking deluges after Christmas, and floods in Auckland.

Eight named tropical cyclones have occurred north of New Zealand, two of them in February. Weatherwatch has predicted that another large cyclone could form in the Coral Sea this weekend and bear down on New Zealand by the middle of next week.

La Nina is also blamed for a big increase in common household flies in Auckland and the proliferation of microscopic jellyfish along the region's eastern beaches, which prompted health warnings after bitten swimmers reported unbearable itchiness.