Low visibility and icy roads helped land some motorists in the ditch. (CBC)

Fog and ice have forced the closure of a 150-kilometre stretch of the Trans-Canada Highway in Saskatchewan between Swift Current and Moose Jaw.

Bad weather rolled into Saskatchewan Tuesday afternoon and produced treacherous driving conditions throughout the province.

"A vigorous disturbance ... from British Columbia has spread freezing rain and ice pellets into parts of southwestern and south-central Saskatchewan," Environment Canada said Tuesday evening in an updated weather warning.

Forecasters said the precipitation would turn into snow overnight.

Snowfall amounts of 10 to 20 centimetres are expected by Wednesday morning.

By midafternoon Tuesday, RCMP said they were responding to reports of cars that had slid off the Trans-Canada Highway east of Regina.

The going was also slick on city streets.

In Saskatoon, slippery roads were blamed in a collision involving a pedestrian in his 70s and a car, police said. The man was taken to hospital with what police described as serious injuries.

Saskatchewan's Highways Hotline reported the closure of the Trans-Canada Highway around 8:30 pm. CST. It did not say when the route would re-open.

The Trans-Canada was not the only major road affected by weather conditions.

The Hotline also reported that visibility was reduced on many major routes because of blowing snow.

Travel was not recommended on roads around Saskatoon and Regina.

Zero visibility was also reported in the Weyburn area.