Four people, including three children, are dead and five more are fighting for their lives after one of the worst traffic accidents the county has seen for many years.

The scene on Oxford's Eastern Bypass was described by an ambulance chief as one of "tragedy and utter carnage".

The children who died were all travelling to a birthday celebration. Four more children in the same car are in hospital with life-threatening injuries, including the boy celebrating his birthday.

The crash, which involved five vehicles, happened at about 7.30pm on Saturday (May 28) on the A4142 when the driver of a gold Citroen Xsara carrying the birthday group crossed the grass between the two carriageways and collided with oncoming traffic.

The incident happened halfway between the Headington roundabout and the junction with Horspath Driftway. That entire section of the ring road was closed for more than 17 hours while police examined the scene.

The three boys who died were Josh Bartlett, of Blackbird Leys, Liam Hastings, of Rose Hill, and Marshall Haynes, of Headington. All were 13.

The 21-year-old driver of the Honda, Howard Hillsdon, of The Garth, Yarnton, died at the John Radcliffe Hospital.

Damian Jolly, director of operations for Oxfordshire Ambulance Trust, described the collision as "horrendous".

He said: "The scene was one of tragedy and utter carnage. It's the worst traffic incident we have had in Oxfordshire for many years and not something we'd like to see ever again."

After crossing the central verge, which does not have a crash barrier, the Citroen collided with a Honda Civic travelling in the opposite direction.

Two of the children were pronounced dead at the scene, and the other died soon after arriving at the John Radcliffe Hospital.

The other four boys were taken to the JR with life-threatening head injuries. Their condition is said to be critical.

The 45-year-old woman driver of the Citroen, whose critically ill son had his 13th birthday yesterday (Sun May 29), was airlifted to the Great Western Hospital in Swindon where she is in intensive care being treated for multiple injuries, including severe neck injuries.

A male passanger from the Honda was airlifted to Stoke Mandeville Hospital in Aylesbury. His injuries were said not to be serious.

A further two vehicles travelling northbound were involved after the initial collision. The lone male drivers of an Audi and a Volkswagen were both treated for minor injuries at the scene and at The Horton Hospital, Banbury.

A motorcyclist who swerved to avoid the collision suffered minor injuries. The driver of a VW Polo was unhurt after his car, travelling southbound, was damaged by flying debris.

Police Superintendent Mick Doyle said the investigation would take many weeks to complete, but said: "A Citroen Xsara is not designed to carry that number of people. It will be one of many things we will have to investigate.

"This incident has been challenging and distressing for all involved and my officers continue to work to establish what happened.

"This remains our focus in the coming days and we are also working to support the family and friends of those involved. They have our deepest sympathies."

Bill Baker, deputy leader of Oxford City Council, said he was saddened by the crash.

He said: "I was really shocked -- it must be one of the worst crashes in Oxford for quite some time.

"I'm at a loss for words really. It's such a waste of young lives."

The southbound carriageway was reopened at 10am yesterday (Sunday)and the northbound at 1.30pm, after specialist police investigators worked through Saturday night at the crash scene.

Police are appealing to witnesses who have not yet come forward to do so. They also urge anyone who may have information about the vehicles involved before the collision occurred to call them on 0845 8505505.