UPDATE: A TOTAL fire ban has been declared and danger ratings upgraded as Victoria braces for temperatures of up to 44C tomorrow.
No fires can be lit in the open air from midnight as emergency crews prepare for a scorcher, and the longest stretch of extreme heat since 2009's Black Saturday.
An "extreme" fire danger rating has this afternoon been issued for the Wimmera, South West and Central regions.
The danger is "severe" elsewhere.
It comes as an uncontrolled blaze threatens the historic Tasmanian town of Richmond with residents being urged to leave immediately.
Country Fire Authority state duty officer Tony Bearzatto urged Victorians to have their bushfire survival plans ready and to monitor conditions.
He warned residents trying to complete last-minute burn offs that the opportunity had now passed.
"They should not be burning off," Mr Bearzatto said.
"Keep it for another time when the conditions are more favourable."
Firefighters have been battling a handful of grassfires today but all are under control.
Emergency authorities are completing last-minute preparations.
Mr Bearzatto said this morning about 8000 firefighters from the CFA, Department of Sustainability and Environment and Metropolitan Fire Brigade were on standby.
Forty aircraft, including two aircranes, are also ready to be called into action.
He said while no total fire ban had been declared in Victoria today, most regions had fire restrictions.
Temperatures had climbed into the mid-30s in many areas of the state's west by 4pm.
Horsham peaked at 39.2C at 4.21pm, but had dropped back to 37.9C at 6pm, while Mildura reached 40C at 5.05pm, before cooling off slightly to 38.6C an hour later.
Melbourne hit a high of 37.1C by 4.30pm - only dropping to 36.3C at 6pm - after staying relatively cool for the morning.
Mr Bearzatto urged Victorians to avoid doing anything that might spark a fire, particularly farmers using machinery for harvesting.
"Today's very hot statewide, with fire danger ratings high to very high in most parts of the state," he said.
"Tomorrow we're expecting hotter and drier and windier conditions with extreme fire danger ratings in the southwest and the Wimmera area, which is the first for the season, and severe fire danger ratings for the rest of the state, except east Gippsland."
Fire Services Commissioner Craig Lapsley has warned Victorians to stay alert as the danger intensifies, but insisted the state was in a strong position should an emergency arise.
"The fire services are well prepared, well equipped, and ready to go," he said.
Tomorrow is shaping as the day of greatest risk.
The heatwave tomorrow will force Australia's best road cyclists to get out of bed two hours earlier.
Stage one of the Herald Sun Tour, following today's opening prologue in Williamstown, will start at 9.30am instead of 11am to protect the riders from the worst of the day's conditions.
Another event, a junior lifesaving carnival at Torquay, for more than 1200 competitors and their families, has been postponed.
Mr Lapsley said strong northerly winds of up to 50km/h, bringing "superheated" air from central Australia, posed a significant fire threat.
"The northern winds are the hot winds and obviously are more fierce," Mr Lapsley said.
"That's why Friday is a critical day. Wind is the driving force of how fires move fast."
State agency commander Darrin McKenzie said the work, begun in July, aimed to protect towns and critical infrastructure.
"Strategically it's very useful to slow or stop the progression of fires," he said.
Victoria's northwest is expected to cop the brunt of the hot blast - some experts are tipping extreme temperatures for at least nine days straight.
Weather bureau senior forecaster Dean Stewart said Mildura should expect maximums of 40C or above until at least Tuesday.
It would be the longest heatwave since early 2009, when Mildura recorded 12 consecutive days above 40C.
"It's shaping up to be the longest spell of above 40C days since Black Saturday, but it's nowhere near those kind of conditions at the moment," Mr Stewart said.
A cool southwesterly change should bring relief to southern Victoria late tomorrow, but it will be short-lived.
Read more on the Herald Sun.