In a video posted to Twitter on Monday, Ontario Provincial Police Sgt. Kerry Schmidt said the truck rolled over just north of Aurora Road.
The northbound lanes have been blocked, Schmidt said, adding that the southbound lanes are moving “very slow.”
He said northbound traffic is being directed off the highway at Aurora Road.
According to Schmidt, officers are looking for a burgundy-coloured passenger vehicle, that apparently cut the truck off.
Schmidt said it was raining and the roads were wet at the time of the incident.
“The driver of the truck here lost control, went into the concrete walls in this construction zone, (and) ended up on its side,” he said.
Schmidt said the truck was leaking diesel fuel.
He said absorbent material had been placed on the spilled fuel, adding that was the reason for the delays.
Anyone with information is asked to contact police.
In an update just before 3 p.m., Schmidt said sanders and sweepers were at the scene and were working to clean up the diesel spill.
Schmidt said the cement barrier wall also needed to be repaired before lanes can be reopened.
He estimated that it would take two to three hours to fully clean up after the collision, but said officers hope to have one lane of traffic re-opened within around 90 minutes.
“Progress is being made, it will take some time,” he said. “It’s going to be a tough afternoon rush hour as cleanup is continuing here.”