Police are investigating after four prime movers and a truck and trailer were destroyed by the suspicious fire at the business on Boundary Road in Braeside, about 1am.

"Four trucks have been burnt out and a fifth truck and car sustained heat damage," a police spokeswoman said.

"No one was injured. At this stage the fire is being treated as suspicious. Arson chemists will attend the scene today."

Two people working inside a factory at the site were evacuated safely.

A Metropolitan Fire Brigade spokesman said they received many calls to alert them about the blaze, which was brought under control in about 30 minutes.

Firefighter Keith Pakenham praised crew members for their work in containing the fire to the trucks.

"The warehouse was only about 10 metres away, so it could have been a lot worse," Mr Pakenham said.

Springvale Country Fire Authority incident controller Bernie Frawley said fire crews "did an amazing job protecting the factory and other vehicles from going up in flames as well".

Police and fire investigators continue to investigate the cause.