The motorway was initially closed, but all lanes are now open, with queues going back to Rivington Services following the incident at about 1.30pm today.
Four vehicles were involved in the accident, according to the Highways Agency, with delays of up to an hour expected for motorists in the area.
The man driving the van has been taken to hospital as a precaution, but his injuries are not thought to be serious.
Tailbacks are forming as cars are being directed off the motorway at junction 6 near the Macron Stadium.
The Highways Agency expects normal driving conditions to resume at about 4pm.
A police spokesman said: "The southbound carriageway is closed for the time being as the van has flipped over.
"It has not been possible to get any cars past it."