VicRoads says both lanes will reopen when the clean-up is complete.

"The Department of Transport thanks motorists for their patience and safe driving during this disruption," it said in a statement.

UPDATE, 12.20pm: Detours continue near Ballan after the supermarket truck fire almost nine hours ago on the Western Freeway.

In a statement, VicRoads says the Melbourne-bound lanes should re-open later this afternoon.

Clean-up crews continue to to empty the B-Double, which was carrying a full load of eggs and biscuits.

A crane is en route to help load the damaged trailers on to heavy haulage trucks as they cannot be towed.

The road surface will then be inspected and any damage will be rectified.

EARLIER: The Western Freeway remains closed Melbourne-bound at Ballan due to a truck fire overnight.

It is understood a supermarket truck caught fire near the Ballan-Daylesford Road exit just before 3.30am.

Melbourne-bound traffic is being directed off the freeway at the Gordon exit, to then use Old Melbourne Road and Geelong-Ballan Road to return to the Western Freeway.

Drivers heading to Melbourne this morning can expect some delays.

VicRoads said while the fire is under control, an extensive clean up continues to remove the truck and inspect the road surface.

"The inbound lanes of the Western Freeway will re-open once it is safe to do so. Outbound lanes remain open," A VicRoads spokesperson said.

Ballarat City Fire Station said the fire was brought under control fairly quickly while Ambulance Victoria confirmed there were no injuries from the incident.

For the latest traffic information around the state visit traffic.vicroads.vic.gov.au

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