Over the last few days, Ontario Provincial Police say there have been three instances of cinderblocks being thrown onto Highway 401 traffic from overpasses.

Two of instances happened on Wednesday, said Sgt. Kerry Schmidt in a livestreamed video. The first, around 11:15 a.m., was allegedly at the Yonge Street overpass. Around an hour later, he said another witness reported something similar further east at the Warden Avenue overpass.

And on Sunday night, there was another incident around 10 p.m. when a vehicle travelling on the 401 was hit by a cinderblock in a bag, allegedly thrown off the Progress Avenue overpass in Scarborough.

"When people are throwing not just bricks, but full cinderblock pieces of cement off of an overpass onto traffic below, the results can be absolutely deadly and catastrophic," Schmidt said.

The suspect from the Yonge Street incident was a man, but there is no suspect information available for the other two incidents.

Schmidt said police are hoping to bring this to an end "before someone gets hurt or killed."

"This is not just mischief," he said. "This is criminal negligence."