Six people have been injured in a “serious collision” between a minibus and a lorry on the M4.
The crash happened at about 12:20 BST on the eastbound carriageway between junction 14 at Hungerford and junction 13 at Newbury.
South Central Ambulance Service said three people in the minibus had been taken to hospitals in Oxford and Bristol with life-threatening injuries.
The eastbound carriageway is expected to be blocked for “many hours”.
Three other people in the minibus suffered less serious injuries and were taken to hospitals in Swindon and Reading, the ambulance service said.
The westbound carriageway was closed to allow three air ambulances to land but has since reopened.
Two of the seriously injured were flown to major trauma centres at the John Radcliffe Hospital in Oxford and Bristol Southmead Hospital.
The third was taken by road, also to the John Radcliffe.
Thames Valley Police have advised motorists to avoid the area if possible.
James Lloyd, who passed the scene shortly after the crash, said a large articulated lorry had gone into the back of a minibus.
The force of the impact had shunted the minibus between about 100 yards along the carriageway, he added.
Dominique Hamblin tweeted: “I have never seen an accident site so horrendous looking and with such an enormous emergency services response as on the M4. Looked nasty, I pray it’s not that bad.”