The OPP closed parts of Highway 402 early Thursday afternoon after multiple collisions and zero visibility caused by blowing snow.
Provincial police are reporting an 11-vehicle collision in the westbound lanes just east of Nauvoo Rd. occurred just after 1 p.m.
At the time, the weather was so bad two air ambulances had to be parked on Highway 402 at Centre Rd. (Highway 81), waiting for the injured to be transported to them by land ambulance.
Early reports indicate that four people were transported from the area to be treated for undetermined injuries.
Subsequently, about 100 vehicles trapped on the highway behind the collision were re-routed.
Police say the westbound lanes of the 402 are expected to remain closed for "a considerable amount of time."
Lambton OPP say no vehicles will be towed out of ditches or off the highway until it is safe to do so and motorists are being asked to avoid the area.
Frigid temperatures forecast
Meanwhile another cold weather alert has been issued by the Middlesex-London Health Unit as frigid temperatures hit the region.
Environment Canada was calling for temperatures around -15 C Thursday afternoon, with wind chill values near -30 C.
Daytime lows over the next few days are also expected to remain in the -20 C range with bitterly cold wind chills.
The health unit's cold weather alert takes effect Thursday afternoon and continues until Tuesday, when highs are expected to be closer to -8 C.
This is the sixth cold weather alert issued in 2015, and comes over what is for many the Family Day long weekend.
Iqbal Kalsi, environmental health manager at the health unit, says, "Heading into the long weekend, it’s important to consider the weather if you’re planning outdoor activities like skating, skiing or sledding. Spending the day enjoying the outdoors is great, as long as you plan for the conditions."
Environment Canada has also issued a number of snow squall watches and warnings for the region.
The forecaster says lake effect flurries and local snow squalls have developed over Lake Huron in a northwest flow.
Areas between Goderich and Grand Bend and in eastern Lambton County were being hit Thursday morning, and the snow could travel as far south as Elgin County.
Local accumulations of up to 10 centimetres per 12 hours are possible, along with poor visibility in snow and blowing snow.
Snow squalls can cause conditions to change quickly and vary considerably over short distances and drivers are reminded to adjust their driving to the road conditions and consider postponing non-essential travel.
