"Extreme" weather has caused multiple crashes on the M5 near Bristol including a five-car pile-up as vehicles "skidded around" on the road.
Downpours of rain, hail and sleet overnight have caused several roads to freeze, Avon and Somerset Police said.
The M5 has seen closures on both its north and southbound carriageways due to a crash involving five vehicles and an overturned lorry.
A police spokesman said it was not believed anyone was seriously hurt.
The five-car crash happened at about 07:00 GMT and closed the southbound carriageway of the M5 between junctions 14 and 15 in South Gloucestershire.
A lorry earlier overturned at around 05:40 between junction 19 and 20 at Portishead and Clevedon, partially closing the northbound carriageway and causing long tailbacks.
There have also been reports of crashes at junction 1 of the M48 as it joins the M4, and between junctions 17 and 18 of the M5, the police said.
Gloucestershire Police is also dealing with an incident on the M5 in which one person has suffered "serious injuries", after two lorries crashed on the southbound carriageway between junctions 13 and 14.
A spokesman added: "The carriageway has been closed which is causing delays. At this stage it is not known how long closures will be in place for."
Avon Fire and Rescue Service and South Western Ambulance Service have said on Twitter they are attending multiple locations.
Travel Update: The #M5 northbound in South Gloucestershire is CLOSED between J15 (#M4) and J14 due to a serious collision.— Highways England (@HighwaysSWEST) January 21, 2021
On the southbound, traffic is also being held between J14 and J15 due to a separate collision. There are severe delays on approach to this incident. pic.twitter.com/ewpx1LOnHj
A spokesman for Avon and Somerset Police said that where "rain, hail and sleet" had fallen overnight, this was freezing and "causing a lot of vehicles to skid around".
"We are currently dealing with multiple collisions," he said.
"While a number of people have been injured it's not believed anyone is seriously hurt.
"Motorists are advised to take care and drive to the conditions."
Good morning from the South West Regional Operations Centre. We are seeing some quite extreme downpours of rain, Hail and sleet across the network. This is likely to be the case throughout the day. Please stay safe, be cautious and drive to the conditions. pic.twitter.com/XNj2nL0lOY— Highways England (@HighwaysSWEST) January 21, 2021
On Twitter, Highways England added: "We are seeing some quite extreme downpours of rain, hail and sleet across the network. This is likely to be the case throughout the day. Please stay safe, be cautious and drive to the conditions."