An elderly man and woman are dead after the tailgate on a dump truck flew off and slammed into a vehicle on Highway 400 on Saturday afternoon.

Ontario Provincial Police said the dump truck was travelling south when it lost control and slammed into the centre median near King Road at about 2 p.m.

The impact ripped the tailgate from the large truck, sending it into the northbound lanes, where it crashed through the windshield of a Chevrolet Avalanche, said Const. Dave Woodford.

The occupants of the Chevrolet, a man and woman both aged 75, were pronounced dead at the scene.

"You don't expect something like that to happen," Woodford told CTV Toronto. "We hear sometimes tires coming off, but I've never heard of a tailgate coming off a vehicle."

Police closed all lanes of the highway in both directions to investigate and clean up the accident.

Woodford expected the highway to remain closed until at least 8 p.m.

Police are asking witnesses to contact Aurora OPP at 905-841-5777.

With a report from CTV Toronto's John Musselman