Treacherous driving conditions resulted in a series of collisions on Highway 401, including a number of jackknifed trucks that temporarily closed the eastbound lanes at the Brighton, Ont. exit.

After several hours of blockages and detours, parts of Highway 401 eastbound have re-opened, Northumberland County officials say.

Ontario Provincial Police said they have opened the lanes from County Road 30 in Brighton to Division Street in Cobourg. All eastbound lanes at County Road 28 in Port Hope are still closed as reconstruction officers finish an investigation into a single car crash that happened earlier in the day.

Northumberland Paramedics said most of the injuries sustained in the crashes were not serious.

“Mostly bumps and bruises, thankfully,” said EMS Chief Tarmo Uukkivi.

However, further west along the highway, near Port Hope, one person suffered critical injuries when a truck lost control and smashed into a guard rail.

Police shut down the highway in both directions due to weather-related collisions, including one which involved at least 25 vehicles, just before noon on Friday. The westbound lanes were re-opened earlier this afternoon.

An aerial view of the multi-vehicle pileup show a number of transport trucks involved in the collision. OPP Sgt. Peter Leon says six people were injured in the collision and are being treated for minor injuries.

Police say the series of crashes occurred during white-out conditions.

"Once again a little snowfall, windy conditions and black ice has resulted in dozens of collisions and vehicles in the ditch today along stretches of Highway 401 between Brighton and Port Hope," OPP said in a statement.

Environment Canada has issued a snow squall warning for the Trenton area. Some drivers are reporting they have been stuck in traffic for as long as 40 minutes.

Uukkivi said drivers should be very cautions, go slow and leave lots of space between vehicles.

With a report from CTV Toronto’s Tamara Cherry

The OPP says at least seven tractor trailers have jackknifed after the series of crashes on the eastbound 401.

With files from The Canadian Press