Drunk driving may have been the trigger for a chain reaction accident involving an ambulance on highway 20 early this morning. 

Police say it happened at about 3:30 am. A vehicle was rolling westbound on the 20 when the driver hit a traffic sign around the Cartier exit. He was stopped in the left-hand lane when another car stopped to help. 

Moments later, an ambulance came from behind and triggered a chain reaction.

"The ambulance was on their break, so they weren't on a call, and they hit another vehicle already immobilized on the side of ther road," explains Urgences Santé spokesperson David Sasson. 

The ambulance then caught on fire, possibly caused by oxygen tanks inside the ambulance. The paramedics made it out on time. Sasson says they were transported to hospital to be checked. There were no major injuries. 

Provincial police spokesperson Christine Coulombe says the driver of the first car is suspected of drunk driving. 

"Maybe he will face charges for driving under the influence," she says.

The collision closed both sides of the highway at Cartier for a while, but re-opened in time for rush hour.