Australian Prime Minister Scott Morrison has announced 3,000 reserve troops will be deployed to help tackle raging bushfires across the country.
Defence Minister Linda Reynolds said this is the first time this has happened in Australia’s history.
Temperatures have surpassed 40C (104F) in parts of south-east Australia. Officials had warned that Saturday was set to be a “dangerous day”.
Since September, fires in Australia have killed at least 23 people.
Speaking at a press conference on Saturday, Mr Morrison told reporters: “We have seen this disaster escalate to an entirely new level.”
An emergency warning was issued for areas of eastern Victoria that told remaining residents it was now too late to leave.
“The safest option is to plan how you will safely take shelter indoors as conditions worsen,” the warning said, adding: “Leaving now would be deadly.”
Residents were instructed to attempt to take shelter indoors or in a large clearing or body of water.
Dozens of people are missing and some 1,500 homes have already been lost this fire season.
Mr Morrison also announced $20m (£10m) has been allocated to lease four water bomber planes. Defence force bases would provide temporary accommodation, he said.
Authorities in south-east Australia are bracing for a weekend of high temperatures and strong winds, which are threatening to worsen bushfire conditions across the country.
In Victoria, three fires have converged overnight becoming a 6,000-hectare blaze.
The state has already declared a disaster in areas that are home to some 100,000 people and it had urged residents to leave. Twenty-one people remain unaccounted for in Victoria.
Residents in areas under emergency warning have now been told they cannot leave. Areas affected include parts of the Snowy Mountains.
Phone lines are down in some areas of the state.