Australian authorities say an "unprecedented" number of emergency-level bushfires have threatened the state of New South Wales (NSW).
More than 90 blazes were raging across the state on Friday.
Gusty winds and up to 35C heat have exacerbated the fires, many of which are in drought-affected areas.
There are reports of people trapped in their homes in several places, with crew unable to reach them due to the strength of the fires.
"We are in uncharted territory," said Rural Fire Service Commissioner Shane Fitzsimmons, with at least 17 blazes at the highest threat level.
"We have never seen this many fires concurrently at emergency warning level," he said.
What's the latest?
Authorities have deployed more than 1,000 firefighters and 70 aircraft to save "as many people as possible", Mr Fitzsimmons said.
The Rural Fire Service tweeted on Friday that "due to the size and speed of the fires we couldn't get to everyone, even by road or helicopter".
Some people were warned to seek shelter from fires rather than flee, as it was now too late to leave.
Emergency warnings were also issued on Friday for bushfires burning in Queensland and Western Australia.
In NSW, the worst-hit state, crews have fought hundreds of fires since September. Last month, two people died while trying to protect their home.
Last week, one blaze burnt though 2,000 hectares of bush which contained a koala sanctuary. Hundreds of the animals were feared to have died.
What about the drought?
Rains lashed NSW earlier this week, providing much relief to farmers. But the storms were not nearly enough to end the long-running drought.
Authorities in the state warn that many fires will continue to burn unless there is more rain.
"We just cannot overstate the profound impact that the drought is having on fire behaviour," Mr Fitzsimmons said.
Water-bombing aircraft are often flying long distances because of the difficulty of accessing water in dry areas. In some cases authorities have drilled bores to keep up with demand.
"We've very mindful of the scarcity of water and how precious it is but the reality is we can't do fire fighting without water," Mr Fitzsimmons said.
Last week, Sydney was blanketed by smoke for days due to fires in Port Macquarie – a region 380km away.
The poor air quality prompted health warnings for those with asthma and other respiratory problems.
Is this linked to climate change?
Australia's fire season risks growing longer and more intense due to climate change, according to scientists.
Authorities said they were concerned about the severity of the fires ahead of its hottest months, a year after the nation experienced its warmest summer on record.