On Wednesday, authorities urged hundreds of thousands of residents in Australia's southeast to evacuate due to an intense heat wave, warning of the potential for further spreading of a massive bushfire in Victoria, experiencing its most severe conditions in four years.

According to Daily Sabah, 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 45 degrees Celsius (113 degrees Fahrenheit), the Bureau of Meteorology said.

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

"Today will be a very challenging day for firefighters," Jason Heffernan, Chief Officer at 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, 95 kilometers (60 miles) west of Melbourne. The fire, burning since last Thursday, has already destroyed six homes, killed livestock and burnt more than 20,000 hectares (200 square kilometers).

A heat wave is set to sweep in from Australia's outback interior, moving across Victoria before 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 forecast from 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.