SYDNEY, Australia — Tens of thousands of residents in Australia’s southeast were told to evacuate on Wednesday due to an intense heat wave that authorities said could further spread a massive bushfire in the state of Victoria, which faces its worst conditions in four years.

Extreme fire ratings have been issued for large parts of Victoria with the Wimmera region in the west given a catastrophic ranking, the top warning level. Mildura, a rural city of about 56,000, could touch 113 degrees Fahrenheit, the Bureau of Meteorology said.

A potential fire impact zone that covers several rural towns has been identified as officials urged around 30,000 residents there to leave their homes by Wednesday morning.

“Today will be a very challenging day for firefighters,” Jason Heffernan, chief officer at the Victoria Fire Department, told ABC television. “Today is one of those days when communities may need to take immediate action at very short notice.”

Hundreds of firefighters were still battling a massive blaze near the city of Ballarat, 60 miles west of Melbourne. The fire, burning since last Thursday, has already destroyed six homes, killed livestock and burned almost 50,000 acres.

A heat wave is set to sweep in from Australia’s outback interior, moving across Victoria before most likely shifting east to the state of New South Wales on Thursday. Total fire bans are in place across several cities, including Melbourne.

Dry lightning could spark new fires while strong winds that are forecast starting Wednesday afternoon could spread the existing one near Ballarat, Heffernan said.

Heffernan urged people to reconsider any decision to stay back to protect their homes.

“Unless your property is immaculately prepared and you have firefighting resources available and you are fit and you are mentally capable to sustain a long duration firefight … my strong advice to the community is to leave early,” he said.