Traffic is flowing again on the Casco Bay Bridge after a crash in one of the in-bound lanes jammed traffic in South Portland and snarled the morning commute, police said.

The 8:30 a.m. incident involved a tractor trailer and two cars on the Portland side of the span, said South Portland Police Lt. Todd Bernard.

“Traffic is flowing smoothly now in South Portland,” Bernard said. “We’re back to regular heavy traffic. Just usually not this late, there’s still a residual from that (crash).”

It was unclear what caused the collision, but police said there were minor injuries to an unknown number of people.

All of the vehicles had to be towed from the scene.

South Portland police diverted traffic from the bridge while first responders cleaned up, causing significant backups.