A harvester fire caused $420,000 damage at Glenroy on Monday afternoon.

CFS crews were called to the Riddoch Highway at 3.45pm after the machinery caught fire and the flames spread into a wheat crop.

Three CFS trucks and a bulk water carrier were supported by two fire bombers which completed two drops.

A CFS spokesperson said the farmer created a fire break using a nearby tractor which helped to crews to minimise crop damage.

Machinery damage was estimated at $400,000, with another $20,000 in lost crop.

The harvester was carrying seven tonnes of wheat.