Firefighters have extinguished a car fire on the Federal Highway overnight.

At about 1.45am, ACT Fire and Rescue were called to reports of a car fire on Federal Highway at the Gungahlin Drive overpass.

Firefighters quickly extinguished the fire and prevented its spread into nearby grassland.

The on-ramp and one lane northbound on the Federal Highway was closed for about an hour.

The cause of the fire has been deemed suspicious and is being investigated by ACT Policing.

Anyone with further information is urged to contact Crimestoppers on 1800 333 000.