Police have closed the M5 between junctions 7 and 8.
A witness at the scene said it looks like a lorry has jack-knifed and pushed two cars through centre barriers onto the other side of the motorway.
Trevor Harker said: "The side with the accident is not going anywhere for a few hours at least. We spoke to the guys and all people are safe and have been seen by an ambulance.
"Traffic travelling towards Cheltenham is at a standstill. I've never seen so many police cars in one area."
LATEST ON THIS CRASH: Four casualties
A spokesperson for West Mercia Police said: "Emergency services are currently responding to a collision on the M5 between junctions 7 and 8.
"The incident involves a lorry which has collided with the central reservation.
"Lanes are closed southbound and the northbound carriageway has a single lane running past the scene."
Highways England tweeted: "The southbound carriageway M5 J7 Worcester South to J8 M50 link is still blocked.
"We have closed the M5 at J7 southbound. The northbound still has a single lane running past the scene expect delays on approach."
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