An investigation is underway today into the cause of a crash between a coach and a car which left nine people in hospital and 43 coach passengers as 'walking wounded'.

The road was shut for six hours at the bottleneck at Elveden, near Thetford and hundreds of drivers faced long diversions and huge tailbacks.

A white Scania coach carrying 48 people, mostly teenagers, collided with a black Mercedes at 1.24pm yesterday on a single carriageway section near the war memorial, between the A1101 roundabout and the junction with the B1106.

Campaigners said the accident was further proof of the urgent need for the remaining sections of the main Norwich-to-London artery to be dualled – with the �134m project due to begin early next year.

Of the four people travelling in the car, one was taken to the Norfolk and Norwich University Hospital with serious injuries and the other three airlifted to Addenbrooke's in Cambridge. One casualty was described by police last night as having life-threatening injuries.

Five teenagers on the coach suffered minor injuries and were taken to the West Suffolk Hospital in Bury St Edmunds, with the remaining 43 passengers treated at the scene.

The A11 was closed for more than six hours, causing long tailbacks and delays during a particularly busy time, with the usual rush-hour traffic increased by weekend holidaymakers and music fans heading to Thetford Forest for the concert by classical tenor Alfie Boe.

South West Norfolk MP Elizabeth Truss said she would be writing to roads minister Mike Penning in light of yesterday's events.

She said: 'It has obviously been a very serious accident and I hope all those who were involved recover as soon as possible from their injuries.

'I think it does demonstrate that the road, as it is at the moment, is not fit for purpose. I have spent the day promoting tourism in the Brecks and we want coach-loads of people coming here, so we need this road to be safe for those people.

'The dualling will start some time between January and March, but it has not been precisely scheduled by the Department of Transport. The money has been earmarked, but I do want to hear from the DOT about when that date will be. I will be writing to the minister about this particular accident, and to ask that question.'

Nobody from the coach company, based in Milton Keynes, was able to comment on the crash.

Motorists faced diversions and long delays until the road was re-opened at about 8pm. During the afternoon, there were reports of drivers taking two-and-a-half hours to travel a few miles.

The incident was attended by police, fire, ambulance crews, rapid response vehicles, three air ambulances, and the hazardous area response team (HART).

Neil Storey, interim director of emergency operations for the East of England Ambulance Service, attended the scene. He said: 'Once the scale of what had happened was ascertained, a major incident was declared and ambulance, police and fire colleagues have worked closely together on scene.

'Nine patients have been taken to Addenbrooke's, West Suffolk, and Norfolk and Norwich hospitals, and 43 patients described as 'walking wounded' and following assessments by HART operatives, they did not require to go to hospital. I'd like to thank all of the crews who have worked hard at the scene to safely attend to patients.'

nAnyone who witnessed the crash is asked to contact Suffolk Police on 101.