It follows a sweltering top of 38 degrees yesterday when crowds flocked to the city's pools for relief.

The extreme heat has prompted the CFA to issue a Total Fire Ban across most of the state until the early hours of New Year's Day.

Relief is not expected until lunchtime tomorrow when a cool change will sweep through the state.

Bureau of Meteorology senior forecaster Richard Carlyon said the temperatures for Ballarat for the month were two degrees above the December average and the hottest since 1994.

"Two degrees above the average is quite significant, even though it's not going to be the hottest December ever in Ballarat," he said.

"It's still been well above the average of 22.5 degrees."

Melbourne is expected to break its record for the hottest December on record with a scorching 42 degrees today.

Mr Carlyon said it was difficult to predict whether the heat would continue for the rest of summer.

"The start of January on Sunday will be hot before the cool change comes through," Mr Carlyon said.

"It's hard to say whether the next two months will continue to be hotter than usual, but if temperatures stay close to or above the average in January and February it might be the warmest summer on record."

CFA region 15 operations manager Mick Harris said two days of soaring temperatures put the state at a high risk of fire today.

"We have between 10 and 15 days like this every year but the problem is that we've had two in a row," he said.

"In the early afternoon the fire risk will be extreme in Ballarat."

The CFA took the unusual step of continuing the ban to 4am, rather than stopping at midnight, to ensure people remained vigilant during New Year's Eve celebrations.

Mr Harris warned that fireworks should not be used in celebrations without a permit.

"This time of year people need a permit from us and we won't give that to people unless they have a WorkCover permit.

"We would advise people to take the usual precautions, but also that people should not use fire bombs or other fireworks."

Mr Harris said the CFA would staff the coordination centre throughout the day and night.

Temperatures are expected to reach 27 degrees on Sunday before a cool change with rain.