GUELPH -- A driver has been transported to hospital by air ambulance following a three-vehicle collision on Highway 401 at Guelph Line, police say.

Ontario Provincial Police tweeted about the crash, which happened in the westbound lanes, just after 5 p.m. Tuesday.

Traffic was brought to a standstill for hours, but the lanes were reopened later that night.

Police say a Toyota Yaris was travelling in the left lane and was rear ended by a pickup truck pulling a trailer at a high rate of speed.

The Toyota then reportedly crossed into the middle lane, was struck by a dump truck, went into a ditch, and hit a tree.

The driver was trapped inside the vehicle.

"It was horrendous, it should have been much worse," said Cst. Tim Dunnah of the OPP. "Air ambulance did attend and land at the scene. Extracation of the driver was completed and he was transported by air ambulance to a Hamitlon trauma centre."

Police add that the condition of the man driving the Toyota has since improved from life-threatening to serious.

The driver of the truck has been charged with careless driving.