Police are investigating the cause of a “horrific” crash which left four dead and forced the closure of a busy stretch of motorway.

See also: Wrong way M6 crash horror – in pictures

Traffic was diverted from the scene of the collision, on the M6 southbound near Walsall, for more than seven hours on Sunday when the road was closed between junctions eight and seven.

Vehicles heading north were also diverted for six hours following the two-car crash which happened just before 6am.

The victims, all men who have not yet been named, had been travelling in two cars – a silver Ford Fusion and a Peugeot 406 of the same colour. All four were confirmed dead at the scene, near to the M5 interchange.

Police said the Ford Fusion, carrying a lone driver, was travelling along the motorway in the wrong direction when the crash happened.

The Peugeot contained four men. Three were killed and another was taken to Sandwell General Hospital in a serious but not life-threatening condition.

A spokesman for the Highways Agency said: “One of the cars was travelling northbound on the southbound carriageway. We don’t know how it happened, it is subject to a police investigation.”

He said motorists were alerted to the crash with electronic signs and diverted onto the M5 motorway.

Ch Insp Baljeet Sidhu, from the Central Motorway Police Group, said: “This is a horrific collision which most tragically involved four fatalities.

“We would urge anyone with information travelling on that stretch of motorway at the time to come forward. They may hold vital information to assist with the inquiry.”