Penrith in Sydney's west is the 'hottest place on earth'

Penrith in Sydney's west is the hottest place on the planet right now, with temperatures creeping towards 50C.

Penrith in Sydney's west is currently the hottest place on the planet with sweltering temperatures creeping up to 50C.

The city recorded its hottest ever day with the mercury reaching 48.9C at 3pm, while the Bureau of Meteorology recorded a high of 47.7C at 2pm.

The heat is set to last several hours, with temperatures forecast to stay above 40C until sunset just after 8pm.

According to the website World Weather, the hottest place on earth on Friday was Birdsville Airport in Queensland, where the mercury reached 46.8 degrees.

It comes as suburbs at the foot of the Blue Mountains are on high alert over potential fire risk in today's state of emergency.

A NSW Rural Fire Service spokesman said the threat of the fire's burning in the Blue Mountains and weather conditions on Saturday "places high risk of ember attacks and spot fires on homes surrounding Winmalee, Hawkesbury Heights, Castlereagh and the Penrith region".

Temperatures in inner Sydney have been more than 10 degrees cooler, but still exceeded 35C in some parts of the city.

In this satellite image the Clyde Mountain Fire, 200km south of Sydney, rages. Photo / AP

A southerly change is expected to hit the NSW south coast later this evening, and reach inner Sydney by 11pm.

Extreme weather has been forecast for large parts of Australia this weekend, adding to the bushfire nightmare ravaging several regions across New South Wales, Victoria and South Australia.

It's an unfathomable challenge for firefighters battling what is already the worst season on record, and likely to become even more devastating this weekend.

NEW SOUTH WALES

Temperatures surpassing 40C are set to combine with dry lightning strikes and wind to add to NSW's bushfire nightmare over the weekend.

But a number of days of respite are expected to follow.

Saturday's forecast paints a grim outlook for parts of the state – particularly the NSW south coast – already battling scores of uncontrolled deadly bushfires as residents flee their homes and holiday-goers cancel plans.

A change will sweep over the state later this evening, Bureau of Meteorology acting NSW manager Jane Golding said.

"In short, we've got a long hot day to get through first with some really dangerous fire dangers," Ms Golding told reporters on Friday.

"That cold front bringing that southerly change, we're expecting that not to reach the far south coast … until late in the day, to move through the Batemans Bay region early evening and come through Sydney about midnight."

The fire danger will reach extreme levels in some areas and the forecast late cool change is due to bring thunderstorms and lightning.

The Rural Fire Service said weather conditions around NSW would ease for a number of days from Sunday.

Southern NSW may experience some showers on Sunday and Monday.

"There's potential for some elevated winds later in (next) week but no big heat spikes because of that hot air mass, there's some more moist air brought into the west of the country helping to flush out that hot air," RFS deputy commissioner Rob Rogers told reporters on Friday.

"There's some potential showers Sunday, Monday, particularly in Victoria that potentially might push up to the south of NSW. That'll all be welcome."

NSW Health, meanwhile, warned people to remain cautious about air pollution, with the Sydney basin likely to endure smoke haze on Saturday.

The elderly and those with lung and heart conditions have been advised to remain indoors and avoid exercise.

A view of fire damage in Sarsfield in East Gippsland. Photo / Getty Images

VICTORIA

A gusty southerly change is expected to hit Victoria this afternoon.

But the change won't bring a reprieve from the risk of dry lightning, which Victorian Emergency Management Commissioner Andrew Crisp says could mean new fires.

"Don't just be focused on the fires we've got at the moment. Be thinking about where there would be other fires," he warned Victorians on Thursday.

Mr Crisp said it is also possible some current fires could merge on Saturday or the days to follow, including a blaze in Corryong in the northeast and another in southern NSW.

Total fire bans have been declared on Saturday for the Mallee, Northern Country, North Central, North East, East Gippsland, West and South Gippsland weather districts.

An unprecedented state of disaster was declared on Thursday, triggering powers introduced after the devastating 2009 Black Saturday bushfires, including allowing authorities to compel people to leave.

Areas covered by the declaration are the East Gippsland Shire, Mansfield Shire, Wellington Shire, Wangaratta Rural Shire, Towong Shire and Alpine Shire. It also covers Mount Buller, Mount Hotham and the Mount Stirling Alpine Resorts. Evacuation alerts were in place late on Friday night for blazes near the Buchan Valley, Abbeyard, Bruthen and surrounds, the upper Snowy area, and north of Mount Taylor.

SOUTH AUSTRALIA

An air quality alert has been issued for parts of South Australia because of smoke from a large bushfire burning on Kangaroo Island and raised dust in the north of the state.

After a day of hot and windy conditions on Friday, a cool change was expected to blow smoke and dust over the metropolitan Adelaide and other areas. SA Health said the reduced air quality was expected to persist for the next 24 hours.

Chief Public Health Officer Nicola Spurrier said people with chest or heart conditions were urged to stay indoors and follow their personal health management plans.

"We know that exposure to high levels of smoke and dust can aggravate conditions such as asthma, emphysema, bronchitis and other respiratory diseases," Professor Spurrier said.

"We also know that high levels of dust can be associated with an increased risk of cardiac events such as heart attacks."