The Premier Ted Baillieu has urged Victorians to remain vigilant ahead of more extreme fire weather.

Temperatures are expected to again soar into the 40s in much of the Sate on Thursday.

As authorities brace for another day of extreme fire danger, Police say they are monitoring known arsonists.

There have been a spate of deliberately lit fires in recent weeks, the most recent today, in Geelong.

While police have issued a stern warning to would-be arsonists, the Premier urged Victorians to remain vigilant ahead of more extreme fire weather.

"Over the next two or three days there will be further significant risks," Mr Baillieu said.

"The weather pattern is such that we are likely to experience again significant hot weather, particularly over Thursday and Friday.

"We urge all Victorian's, particularly those in holiday areas and those travelling to make sure they understand the risks involved."

Severe hot weather is forecast particularly in the Wimmera, the south-west central and north-central.

"For those who are travelling in high fire prone fire areas, they need to ensure that they stay in touch with the appropriate agencies," Mr Baillieu said.

The Country Fire Authority's Deputy chief officer Alen Slijepcevic says while a change is expected later in the day, the hot weather is expected to hover in the western part of the State on Thursday night, and continue into Friday in the north-east.

"The landscape is very dry across the State, so when the fires start, they can take a hold and run," he said.

Mr Slijepcevic says there are 8,000 crews stationed across the State who can be readied within minutes.

"We'll have aircraft around the State, and we'll have incident management teams ready to respond, and all agencies will be ready," he said.

Would-be arsonists warned

More than a dozen fires have been deliberately lit across Melbourne in the past two weeks.

The most recent suspicious fire was in Geelong on Tuesday afternoon.

The first of a number of small grassfires near the Barwon River started at around 2:00pm.

The fires broke out between the river and the railway line.

"There is always arson activity in every fire season," Mr Slijepcevic said.

"It becomes a bigger problem when there is underlying dryness in the State and the fuel is dry enough to burn."

Mr Baillieu says anyone who deliberately lights a fire is committing a very serious crime.

"Obviously anybody who lights a fire at any time which endangers life, is not only foolish, they're reckless and they are committing a very serious crime," Mr Baillieu said.

Extra police will be on patrol during extreme temperatures later this week, in areas of Victoria where suspicious fires have started.

Known arsonists will also be closely monitored

Police say there were 195 suspicious grass and scrub fires in December, and they have charged 29 people with arson offences since the start of summer.

Assistant Police Commissioner Steve Fontana says extra officers will be deployed on Thursday when the fire danger rating is expected to reach severe in parts of the state.

"When we are getting into that real extreme weather we scale up our resources, not only with local resources throughout the State, but we have our operational response unit to send patrols up and it's about creating that highly visibly police presence."

Police say there have 195 suspicious fires since December.

"Since the beginning of December we've charged about 29 arsonists across the State," he said.

"I can say a number of them have been teenagers or juveniles.

He says Operation Firesetter will be targeting hot spots, known arsonists, and people they consider to be high risk.

"We might be using physical surveillance or other types of covert surveillance on those people," he said.

While the Commissioner says he does not believe the number of recent attacks are out of control, he does say there is always a spike in such incidents when it is hot.

Many incidents are currently under investigation, including last night's fire at Little River.

The blaze burnt about 500 hectares of farmland and came close to some property.

The rocky terrain meant it took 200 firefighters and four aerial water bombers four hours to get the blaze under control.

Mr Slijepcevic says it is the second suspicious fire in the area in the past few weeks.

"We would like to ask anyone who maybe saw some activities, some illegal activities to report it through crimestoppers," he said.

Victorian Firefighters return from Tasmania

The Premier Ted Baillieu welcomed back 60 of the State's firefighters from Tasmania at Melbourne Airport today.

"We understand how difficult it's been for the last two or three days, and to understand what a fantastic job they have done," he said.

The Premier was in part, referring to the recent death of Peter Cramer who died while battling the Tasmanian fires.

Mr Baillieu spoke Mr Cramer's wife yesterday, and again expressed his condolences.

"He was clearly quite loved," he said.

"Those who I spoke to at Melbourne Airport this morning, a number of them knew him very well."

Mr Baillieu says another 60 Victorian firefighters have been deployed to Tasmania for a week, and any decision to possibly send more will be made in consultation with the Tasmanian Government.

Meanwhile Mr Baillieu says he has received assurances the CFA's fire information website will be able to withstand the demand later in the week.

The CFA site and mobile applications have crashed on recent hot days due to the extremely high user numbers.

"I think that the website provided for 3.5m hits, and that's been significantly expanded and doubled in terms of capacity," he said.

But he says residents in high-risk areas should not rely solely on one source of information.