An air ambulance was called to the M1 in Northamptonshire and the motorway closed after a lorry went through through the central reservation.
The motorway was shut by police after what a spokesman described as a “multi-vehicle” collision south of junction 15 for Northampton at 2.50pm.
The air ambulance has landed at the scene.
The closed stretch, between junction 15 and for the A508 and junction 14 for the A509, is not likely to reopen for several hours.
A police spokesman said: “We would advise anyone heading that way to find an alternative route if possible.”
AA has reported a large amount of “trapped” traffic within the closure.
Eyewitnesses have reported seeing a lorry carrying new vans travel through the central reservation of the motorway.
Mike Cooper, who passed the incident shortly after it happened, said the lorry could have been travelling on the northbound side before crossing over into the opposing carriageway.
He said: “The barrier that separates the north and the south side is smashed completely.
“It looks like a new vehicle carrier has been in the accident.
“There is a car on its roof with the airbags deployed.”
Highways England has reported that the road is not likely to reopen until 2am.