An emergency warning has been issued to residents in central Victoria over an out-of-control bushfire threatening homes and an animal shelter.

The fire is heading towards Cobaw and Lancefield and firefighters have been unable to stop it heading towards homes.

"You are now in immediate danger, act now to protect yourself. Emergency Services may not be able to help you," Emergency Management Victoria's alert says.

The fire has crossed Three Chain Road and is moving fast in a south-easterly direction from Nudist Camp Track towards Maloneys Road and Lancefield.

Spot fires and ember attacks are starting up to 2.5km ahead of the fire front.

Animal shelter Edgar's Mission, near Lancefield, says it has enacted an emergency evacuation plan because the fire is close.

The farm sanctuary has over 250 rescued animals.

"There is a fire in close proximity to Edgar's Mission. Please Do NOT phone us as we are enacting our fire plan. Please do NOT come to Edgar's Mission. Updates as we can," the shelter posted on Facebook on Tuesday afternoon.

Meanwhile, a bushfire that threatened a Bluescope steel plant near Melbourne is being treated as suspicious.

It is the third suspicious fire in Melbourne in 24 hours, with a factory fire at Mordialloc and a fire at AFL superstar Dane Swan's hotel in South Melbourne also being investigated.

Firefighters from 27 trucks fought the fire near the Bluescope plant in Tyabb, getting it under control mid-morning.

Premier Daniel Andrews says emergency services have been pushed during this challenging day, with about 100 fires across the state.

Three are significant fires, the one at Lancefield, one at Yellingbo and one near Creswick.

"It's been a very challenging day and it's not over yet," Mr Andrews told reporters in Melbourne.

"We do hope to have some significant developments in the next couple of hours but the message today is a very clear one - the 15/16 fire season is here now."

A watch and act warning has been issued for Nar Nar Goon North, Maryknoll, Tynong North, where a grassfire is not yet under control.

"Don't wait, leaving now is the safest option - conditions may change and get worse very quickly," the warning says.

There is a watch and act warning also for Strath Creek and for Tonimbuk, Bunyip North, Garfield North, Labertouche, Longwarry North, Bunyip, Longwarry.