Two people died and another two have been seriously injured in a crash involving a lorry and several cars on the M5 in Somerset.
Emergency services were called to the southbound carriageway of the motorway, a mile north of Taunton, at 8.30 BST.
The carriageway has been closed by police between junctions 24, at Huntworth, and 25, for Taunton.
Nearby roads are reported to be very congested and drivers are being advised to avoid the area if possible.
A police statement said two people were pronounced dead at the scene and four other people were taken to hospital.
At least two of those taken to hospital have serious injuries, the statement added.
Insp Frazer Davey, from Avon and Somerset Police, said: "I'm very sad to report two people have lost their lives at the scene this morning.
"There's been a number of other people injured who have been taken to hospital.
"An investigation of this nature will take some time and I'd like to apologise to the number of people caught up in the quite-sizable tailback."
He said the southbound carriageway would remain closed while the circumstances are investigated and any damage to the road surface is repaired.
The northbound carriageway was re-opened at lunchtime after being closed immediately after the crash, but the motorway remains heavily congested in both directions.
In 2011, seven people were killed and more than 50 injured in a crash involving 34 vehicles on the northbound carriageway of the M5 close to junction 25.
Somerset Council said the motorway closure was also causing delays on the local road network, with tailbacks reported on the A358 and along the A38 corridor.