Eight vehicles collided on the E40 towards the coast near the Bruges interchange on Wednesday afternoon, closing all lanes and the hard shoulder and causing major traffic disruption.
The crash happened at about 3.30p.m, Peter Bruyninckx of the Flemish Traffic Centre said.
According to initial reports, several people have been injured, and a medical helicopter has been sent to the scene.
The Traffic Centre said the vehicles involved were six cars and two lorries. It said one car had broken down in the carriageway, and another then crashed into it, triggering a chain-reaction accident.
By about 4.45 p.m, traffic queues were already 10 kilometres long, and drivers heading for the coast were facing delays of more than an hour.
Cars are being diverted off the motorway at the Bruges interchange and routed along a parallel road to the next slip road.
Bruyninckx warned that the disruption would continue to worsen and urged drivers to avoid the route if possible.
He advised anyone travelling from inland areas to the coast later in the evening to take the expressway instead.
