A boy of two was today fighting for his life in hospital after a horrific road crash which left six people dead and another two critically injured.

The youngster was a passenger in one of the four cars which collided on the A23 at Pyecombe yesterday in what has been described as the worst ever road accident in Sussex.

He was today in intensive care at the Royal Sussex County Hospital, Brighton.

A man and woman were critically ill at the Princess Royal Hospital in Haywards Heath.

Three others have been discharged after being treated for minor injuries.

The crash happened at 4.28pm yesterday as day-trippers began making their way home from the coast at the end of a sunny weekend.

A black BMW going south veered out of control, careered through the central reservation barrier and slammed into oncoming traffic.

The occupants of the BMW - two men and three women, all believed to be in their early twenties and all thought to be from Sussex - died at the scene.

The BMW, a Land-Rover Freelander in which a male passenger was killed and a Volkswagen hatchback were ripped apart on impact.

Motorists raced from their vehicles attempting to give first aid. Some ran with fire extinguishers to put out fires, others tried to resuscitate casualties and gave comfort to the injured.

When emergency crews reached the scene they described it as "carnage."

Survivors wrapped in blankets sat at the roadside in shock. There were mangled pieces of metal strewn across the carriageway.

Police began searching hedges while a crane lifted chunks of the cars off the road.

A driver who was travelling home to Brighton from Heathrow said: "As we came down the A23 past Hickstead, I noticed some dust clouds sprout up in the opposite lane. This was followed by a short, sharp plume of smoke.

"The cars in front of us were slowing down rapidly, so I told my girlfriend to take the slip road on the left. Then suddenly the cars were screeching to a halt.

"I looked over to my right and was totally aghast at what I saw. Three cars shunted in half and two so completely destroyed and burnt-out, I couldn't even make out what they were.

"It appears one of the cars had disintegrated going through the barrier and the debris was all over the road.

"One of the vehicles was still burning and some of the passengers from 20 or so cars behind it on the northbound carriageway were running towards it with fire extinguishers trying to put it out. "

Alan Dejongh, a 32-year-old former paramedic from Streatham, South London, was driving home with his girlfriend Helen Mitakidis, a 35-year-old accident and emergency doctor.

He said: "I could see two cars up ahead on fire, a BMW and a Freelander. Members of the public were running over with fire extinguishers. Everyone was helping.

"I tried to resuscitate a woman but, sadly, she died later. I went to my girlfriend who was helping a boy of about three or four. I have seen a lot of horrible things in my job but this crash was an absolute nightmare. The way the public acted, everyone doing what they could, was something else."

Fay Stebbings, who lives in a row of terraced quarry cottages called Donkey Row at Newtimber, about 150 yards away, said: "I was inside reading a magazine when I heard three huge crunches.

"I went outside and there was somebody with a fire extinguisher putting out flames in one of the cars.

"I think it was a silver 4x4 in the middle of the road on fire. Another couple of people were pulling at the front of the car.

"It is horrible to think you are sitting here, you hear a noise and six people lost their lives. I just can't believe it."

A ten-mile stretch of the A23 was closed in both directions overnight from the A27 junction to Hickstead as police cleared the road and began their investigation. It opened again at 8am today.

Thousands of drivers were caught in tailbacks as diversions were set up on surrounding roads. The A27 Brighton bypass was gridlocked for several hours and jams stretched back to the Old Steine in Brighton until 10pm.

The crash was declared a major incident and extra hospital staff were called in to treat the injured. All but emergency operations were cancelled as the county's hospitals were put on alert.

Insp Steve Higgs, of Sussex Police, said: "This is without doubt one of the most serious incidents of its kind to occur in Sussex.

"We are doing everything we can to ensure the bereaved relatives and those involved have answers to the many questions which will arise over the coming days and weeks.

Police appealed for witnesses to call 0845 6070 999.