Fresh emergency warnings were issued at 5.30am on Tuesday for a blaze burning in a northerly direction from Wallan towards Bylands and Kilmore.

A state control centre spokeswoman said 21 houses have been destroyed across Victoria since Saturday, with 15 lost in the Kilmore and surrounding areas.

A further 30 properties have been reported as lost state-wide – including 20 in north of Melbourne – but numbers are yet to be confirmed by the Country Fire Authority.

The fire has spread from Mickleham to Pyalong, north of Melbourne, has jumped the Northern Highway as hundreds of firefighters battle to protect at-risk towns.

The blaze continues to threaten homes on the southern side of Kilmore, but crews have managed to contain the flames charging towards the town's east, from where hundreds of people fled on Monday night.

More than 1000 residents had flocked to take refuge in an open field at Kilmore racecourse by 5pm after evacuations on Monday afternoon, when the fire threat became increasingly worrying.

In its emergency warning, the CFA advised Bylands, Kilmore, Kilmore East, Darraweit Guim and Wallan residents to act now and protect themselves against the massive blaze.

In the Wallan and Darrawit Guim areas, the fire has jumped Old Sydney Road, and is heading towards Wallan.

Overnight, 2500 firefighters battled 19 blazes across the state with the aid of 70 aircraft and interstate and New Zealand firefighters.

Police suspect nine of the state's bushfires in the past few days were deliberately lit. More than 280,000 hectares burnt in more than 150 fires since the weekend.

Police revealed that the arson squad was investigating the cause of 14 grass and scrub fires in the state and had judged nine to be suspicious.

They included blazes next to the Merri Creek at Fawkner in Melbourne's north, on the Great Ocean Road at Port Campbell, at Old Jindivick, in Drouin West, Gippsland, and at Havilah Road, in North Bendigo.

The causes of five other fires, including at Maiden Gully, an outer-western suburb of Bendigo, Mornington and Gisborne South, had yet to be assessed.

In Kilmore, the fire caused panic and triggered an emergency warning to when it crossed Kilmore-Lancefield road near the Kilmore cemetery shortly before 8pm. Almost all cars cleared out of the racecourse en masse within half an hour to head towards Broadford or Seymour further north.

CFA incident controller John Leben said Kilmore residents who chose to remain were still under threat and needed to stay vigilant.

Firefighters battled throughout the night in a bid to protect Kilmore's outskirts and stop the blaze from spreading further north, he said.

Dozens of schools and kindergartens in Kilmore, Wallan and Pyalong will be closed on Tuesday as the fire continues to burn.

Resident Michelle Chamberlain left her home on the town's outskirts on Monday afternoon when the fast-approaching columns of smoke were fewer than half a kilometre from her home. Her husband, Bruce, has stayed behind to hose down the property.

But his car is packed with family photos and valuables so he's ready to leave at a moment's notice.

Ms Chamberlain, who has lived in the area for 17 years, said the whole town was on high alert as the fire closes in.

"My nerves are shocking ... And I have a massive headache with all the smoke,’’ she said.

"We escaped Black Saturday and ad then have had three fires rapt unfounded us but have missed them all. But this is real."

"You hear that?" asks Tracey Dickson, as helicopters clatter and sirens wail beyond the rooftops. "That's how you know it's close."

Ms Dickson and her family were told to evacuate shortly after 5.30pm after being informed their Kilmore hosing estate was in the line of fire.

"We saw the smoke come over with the wind change ... It went probably 15 kilometres in a matter of 10 minutes.

"There are a lot of scared people."

Craig Kneebone said Kilmore residents were better prepared for the threat of fire since a near miss on Black Saturday five years ago.

"Everyone's prepared now. We had a plan and we knew what to do."

Chief Commissioner Ken Lay said police had suspects for some of the fires.

"Some investigations are well progressed. We have a far far better picture than we ever have before on these people and how they behave."

Police were revisiting the homes of known arsonists and patrolling high-risk areas.