A "mega blaze" raging across a 60km (37 mile) front north of the Australian city of Sydney cannot currently be put out, fire officials have warned.
The blaze across 300,000 hectares (1,150 sq m) is just an hour's drive from the nation's most-populous city.
People who cannot defend their property from approaching fires have been told they should leave immediately.
Since October, bushfires have killed six people and destroyed more than 700 homes across Australia.
The severity of the blazes so early in the fire season has caused alarm, and prompted calls for greater action to tackle climate change.
Fires have also raged across Queensland, Victoria, South Australia, Western Australia and Tasmania.
What's the latest on the ground?
Several fires have combined to form the mega blaze north of Sydney, although more than a dozen locations are affected across New South Wales.
At one point on Friday, nine fires had been raised to emergency level warnings, although these had decreased markedly amid a brief respite in conditions later in the day.
The north Sydney blazes were sending black fumes across the city, causing a rise in medical problems.
New South Wales Rural Fire Service (RFS) deputy commissioner, Rob Rogers told ABC: "We cannot stop these fires, they will just keep burning until conditions ease, and then we'll try to do what we can to contain them."
He said the 60km stretch from Hawkesbury to Singleton was "just fire that whole way".
The RFS website listed five fires roughly in a line from Nullo Mountain to Wollombi as out of control at 05:00 local time on Saturday (18:00 GMT Friday), with another out of control at Green Wattle Creek, south-west of Sydney.
Video footage from the Orangeville area showed firefighters running from a wall of fire and the Walkabout Wildlife Park has evacuated hundreds of animals.
The Bureau of Meteorology (BOM) also said that "some fires were too big to put out".
Fire officials in Ingleburn warned: "If your property is not prepared for the bushfire season and you're not sure you are able or capable of defending your property if a fire approaches you need to leave straight away."
Firefighters from Canada were briefed in Sydney on Friday and will be deployed across New South Wales over the weekend, to be joined by teams from the US.
What's the outlook?
There appears to be little respite.
RFS founder and former commissioner, Phil Koperberg, told the Sydney Morning Herald: "People are nervous and they have a right to be… the worst is yet to come".
Tuesday is the next big concern, with temperatures inland of Sydney likely to reach 40C plus.
Some firefighters have expressed concern that volunteer numbers might not be enough and that there are inadequate water supplies.
One said the fires were "all ticking time-bombs – without rain those fires won't be put out".
Sydney may be blanketed in smoke for weeks, if not months, RFS Commissioner Shane Fitzsimmons said.
Is this fire season particularly bad?
It hasn't come close to the fatalities of 2009, when nearly 200 people died, but the scale of the damage has been huge.
More than 1.6 million hectares of land have burned in New South Wales alone.
The season has hit earlier than normal and has been exacerbated by drought conditions.
Mr Fitzsimmons said: "There is an absolute lack of moisture in the soil, a lack of moisture in the vegetation… you are seeing fires started very easily and they are spreading extremely quickly, and they are burning ridiculously intensely."
Is climate change to blame?
The BOM says thRead More – Source