Two people have died and three people are in a critical condition after a serious collision involving a lorry and a minibus on the M4 in Berkshire.

Six ambulances and three helicopters attended the scene after the crash occurred at 12.20pm on Thursday. Thames Valley police said two people in the minibus died at the scene, while seven others – including both drivers – were injured. Of these, three were being treated for critical injuries in hospitals in Oxford and Bristol, three were being treated for non-life-threatening injuries in Swindon and Reading, and the driver of the heavy goods vehicle was also taken to hospital with minor injuries.

Thames Valley police said on Thursday evening that the eastbound carriageway between junction 14 at Hungerford and junction 13 at Chieveley would remain blocked for several hours and officers were “working to turn affected motorists around”. Diversions were in place, but the surrounding roads remained busy.

The westbound carriageway was closed to allow the air ambulances to land but had since reopened and traffic was moving.

Two rapid response vehicles, two hazardous area response units and the Royal Berkshire fire and rescue service were also dispatched to the scene.

One motorist, James Lloyd, described the seriousness of the crash in a tweet: “M4 closed due to worst accident I’ve ever seen in many years of driving.”

Karen Romeis, who was stuck in queues on the eastbound M4, tweeted that motorists were getting out of their cars and walking over to the opposite carriageway. “Apparently we’re going to be here for several hours yet.”

Thames Valley police also appealed for witnesses and anyone who had dash-cam footage to make contact.