Firefighters believe there is no one inside the single storey brick veneer on George Street, Doncaster, but they are yet to gain entry into the burning building.

"It's fully involved and the ceiling is collapsing," an MFB spokeswoman said.

"Firefighters will conduct a search when they can."

The calls from passers-by came rolling into Triple 0 from about 9.30pm with the fire visible from the busy Williamstown Road.

Seven fire trucks were initially sent to combat the fast-moving flames.

"We had a strong attack on the fire very early," the spokeswoman said.

At 10.25pm, the fire was not yet under control.

It is too early to tell what sparked the blaze.