VANCOUVER -- A 49-year-old man is in hospital in serious condition after an incident involving a Canada Post vehicle near the Massey Tunnel Friday afternoon.

BC Emergency Health Services confirmed to CTV News Vancouver that two ambulances were dispatched to the scene shortly after 1:40 p.m. for reports of a piece of ice that had fallen through a windshield.

Ambulance crews treated one person at the scene and transported them to hospital in serious condition, EHS said.

Video from CTV News Vancouver's Chopper 9 showed a large truck with Canada Post logos being towed off of the highway and onto a side street. The vehicle's windshield was broken on the driver's side, but no other damage was visible.

In a news release, Mounties described the driver as a 49-year-old man from Surrey, and said his injuries are not believed to be life-threatening. They said he was the vehicle's only occupant.

Police said they are investigating the incident and working "to determine the source of the ice." Anyone who witnessed the incident or has dash cam video from the scene is asked to contact the RCMP's Lower Mainland Traffic Services division at 604-526-9744 and cite file 2020-108.

By 4 p.m., the vehicle had been towed away from the area. Photos of the metal grating above the south entrance to the tunnel showed a fair amount of snow accumulated on top of it. It was unclear whether that was the source of the "ice bomb" that fell onto the truck.

In a statement, the Ministry of Transportation and Infrastructure said it has begun "a full assessment" of the incident and is continuing to monitor conditions at the tunnel and working with local police.

"Safety is the ministry’s top priority and our thoughts are with the injured driver at this time," the ministry said.

"Ministry staff and the maintenance contractor have undertaken an initial onsite assessment to ensure the safety of the travelling public. The maintenance contractor has driven all the travel lanes in both directions at the tunnel and can confirm there is no sign of any similar debris. There is nothing that leads the ministry to believe there is a risk, and all lanes of the tunnel remain open to traffic at this time."

The ministry added that an incident of this type is unprecedented at the Massey Tunnel.

"The tunnel has been in operation for over 50 years and we’ve never experienced an event like the one described today," the ministry said. 

Traffic slowed significantly in the southbound lanes of Highway 99 near the tunnel after the incident.

In a tweet, DriveBC advised drivers to expect heavy delays as emergency crews were on scene and the right lane of Highway 99 was blocked. A few minutes later, the agency tweeted that the incident had been cleared, but delays should still be expected.

CTV News has reached out to Canada Post for comment. This story will be updated if and when a response is received.