A LARGE volume of smoke from two grass fires burning near the Bruce Highway north of Brisbane is affecting traffic, with motorists warned to use an alternative route.

Fire crews are at the scene at Dakabin and Elimbah and, while both blazes are under control, smoke is blanketing the northbound lanes of the highway.

Motorists are being urged to avoid the area and to take an alternative route.

There is no threat to property, the Department of Community Safety said.

The delay comes only hours after the Bruce Highway was re-opened following a semi-trailer accident in the southbound lanes at North Lakes at 9.15am.

SEE THE CARNAGE AT THE CRASH SCENE

A semi-trailer struck an overpass and then another truck smashed into the back of it.

The trucks and debris have since been removed and the Anzac Avenue overpass has been inspected by engineers.

SEE THE CARNAGE AT THE CRASH SCENE

One driver received a minor back injury in the crash.

Meanwhile, on the city's southside, commuters travelling along the Pacific Motorway at Eight Mile Plains are experiencing congestion before the Gateway merge.

Medium delays are expected on the highway before the Gateway merge due to a previous crash, with motorists urged to allow extra travel time.

Buses and trains are running to schedule.