The mercury is tipped to hit the high 30s across Victoria on Monday, rising as high as 40C at Mildura in the state's northwest.

A total fire ban has been declared for the Mallee, Wimmera and Northern Country, with the danger rated as severe across the three districts.

Victoria's Country Fire Authority chief officer Jason Heffernan has particular concerns for campers holidaying in regional Victoria and farmers feverishly working to harvest their crops.

"Campfires will not be allowed in the districts from midnight tonight, and we would really urge people not to light one earlier in the night either or in other areas of Victoria," he said.

"Anyone who has had a campfire in recent days should make sure the fire has been adequately extinguished to avoid flare-ups.

"The current hot and dry conditions will allow the finishing of harvest, however I urge those still harvesting to be careful and take all necessary precautions."

The fire danger in North Central, South West, Central and North East regions is considered very high, and high across Gippsland.

A La Nina weather pattern across southeastern Australia has helped to ward off bushfire activity in the fire-hit states of Victoria and NSW this season.

But expected north to northwesterly winds, followed by a west-southwesterly change, dry conditions and an outside chance of some thunderstorm activity has forecasters and fire crews on alert.

Those winds will push down hot air to Tasmania, lifting maximum temperatures 10 to 15C above the January average.

New Norfolk and Richmond are tipped to experience Monday's most extreme maximums of 37C, only two degrees hotter than Hobart's forecast top.

The Tasmanian capital is among 12 municipalities subject to a total fire ban from 2am on Monday, with residents encouraged to avoid travelling to those high-risk areas unless it is critical.

The Tasmania Fire Service has pre-deployed a suite of extra resources, including a number of air water-bombers.

"They'll certainly be our first initial attack and we'll have additional strike teams in position ready to jump on these fires if they start," acting regional chief Ian Bounds told reporters on Sunday.

The fire-friendly hot conditions will be made more complex by 30 to 40km/h winds and possible afternoon dry thunderstorms over southern Tasmania with little or no rainfall.

Meteorologist Luke Johnston says the weather will lift fire danger ratings to severe in the South East and Upper Derwent Valley, and very high for most other parts of the state.

There will be a brief reprieve from the sweltering heat for Tasmania and southern Victoria on Tuesday before the mercury climbs again on Wednesday.

Australian Associated Press