Vic court fire started in airconditioner

A fire at a Melbourne courthouse is no longer being treated as suspicious.

The fire, which caused extensive damage to the Dandenong Drug Court on Monday morning, is believed to have started in an airconditioning unit, the Country Fire Authority says.

The fire had spread "aggressively" through the building and roof space when fire crews arrived.

No one was inside at the time and it was brought under control in 20 minutes with the help of an aerial crew.

Fire investigators traced the ignition point to an airconditioning unit.