Two westbound lanes and two eastbound lanes of Highway 401 just west of Don Mills Rd. have been closed due to a crash involving a tractor-trailer.

The tractor-trailer and a car collided in the westbound lanes around 1:30 p.m. today. The crash forced the rig to hit theoverpass and spill its load of bottled water, OPP Sgt. Sally Stewart said.

One person suffered very minor injuries and did not require treatement at hospital.

A school bus carrying 45 children travelling in the eastbound lanes struck the bottled water debris and received a flat tire, she said.

None of the children were injured but the bus was off to the side of the road.

The OPP expects the lane closings to last for several hoursand to hinder the evening commute. They need a heavy tow truck and cleaning staff to arrive at the scene.

Officers are also waiting for engineers to arrivene to see if the overpass was structurally damaged.