The police have confirmed that several people are dead and 43 have been injured in a horrific pile-up on the M5 near Taunton in Somerset in what is being described as one of the worst crashes in history.

Emergency crews have worked tirelessly through the night to free victims from the crash, which produced a "massive fireball" on the carriageway and involved as many as 27 cars and lorries.

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One witness told Sky News that "a black fog descended" suddenly over the motorway and "the Iceland truck in front of us disappeared".

Avon and Somerset police said on Saturday morning that the casualties ranged from those with life-threatening injuries to the walking wounded.

Assistant Chief Constable Anthony Bangham said some people had been trapped in their burning cars. A number of the vehicles were incinerated. He did not confirm the number of dead.

"At around 8.25pm yesterday there was a multiple collision around junction 25 of the northbound carriageway of the M5," Bangham said.

"The emergency services have been working tirelessly. The incident was very, very challenging and on arrival crews were faced with literally one massive fireball.

"Most vehicles were well alight and most continued to burn for a considerable time. This made it very difficult to search the vehicles. Some of them have been burned to the ground."

Dr Colin Close, medical director for Musgrove Park hospital in Taunton said it was dealing with a range of injuries including limb injuries and complex chest, abdominal and lung injuries.

He said the hospital had dealt with "nothing of this magnitude ever before" and one surgeon was flown by helicopter from the Royal Devon and Exeter hospital to help deal with emergency surgery.

"They have been treated and none are in a critical condition," he added. "Everyone is stable."

Yeovil district hospital said it dealt with 26 "walking wounded" and had discharged 24 of them by Saturday morning.

A man and a boy remain in the hospital but their conditions are not thought to be life-threatening.

"It was a very busy night for us and our staff did really well," said a spokesman.

Avon and Somerset police have released a helpline number for people concerned about relatives: 0800 092 0410.

Local MP Jeremy Browne, said the "scale of the carnage" was "devastating" and the accident had left the Taunton community "numb".

He said he couldn't speculate on the cause of the crash but that the stretch of road was very familiar to local people and although "it didn't involve any twist and turns, it does get foggy".

Browne, who is Liberal Democrat MP for Taunton Deane, said conditions last night were dangerous. It was raining and even when the rain stopped the air was "heavy with mist".

They were the sort of conditions you don't have to find yourself in when you where you can go through a clear patch and the next minute you are in deep fog.

Witnesses described flames more than 20ft high and the sound of several crashes as the incident happened in full view of families attending a large fireworks display [see footnote].

Bev Davis, who lives close to the motorway, told local BBC reporters that she had thought the fireworks display had started again but now realises the cracking sounds were from tyres bursting.

From where we were standing, we could only see what was directly in front of us because the flames and smoke were smothering everything. There must have been 200 metres worth of fire. Plumes of smoke were going up and everything was red.

Tom Evans, who was driving on the southbound carriageway last night, described the crash scene as "harrowing" but said as far as he could tell the night was clear at the time.

He told Sky News:

The smoke from the scene was coming across the motorway but it was clear at the time. I know others say it was foggy, but the heat of the flames may have burned that off. Fire was engulfing two or three of the articulated lorries ... it was very harrowing.

Another witness on the same side of the motorway said he had opened his window to see what was going on but the heat was so intense he was forced to put it up again.

"It is the worst thing I have seen in my life," he said.

The UK has not seen a road traffic accident on the scale of the M5 motorway pile-up since 1991.

Edmund King, president of the AA, said the only comparable incident was a major crash along a stretch of the M4 near Hungerford in March 1991.

It left 10 people dead and a further 25 injured and involved 51 cars.

It happened in heavy fog during morning rush hour after a van skidded into the central barrier of the eastbound carriageway.

At least 16 are feared dead in the 27-car M5 pile-up with the death toll expected to rise further, according to police sources who have been speaking to South West News in Bristol.

Seven people have been killed and 51 injured in a 34-vehicle pile-up on the M5 in Somerset, police have confirmed.

The police revised the number of injured and the number of vehicles involved upwards at lunchtime and confirmed they feared more were dead.

Assistant Chief Constable Anthony Bangham, overall incident commander, said:

Seven people are confirmed to have died as a result of this tragic incident and we do believe there could be more deaths. Our thoughts are with those who may have lost loved ones as a result of last night's collision. A large scale multi-agency operation at the scene continues to remove vehicles, check that there are no other casualties and repair the carriageway. This is a hugely complex operation because of the scale of vehicles and people involved. All vehicles will need to be removed from the scene for forensic examination and this of course takes time. Once the carriageway is clear a large operation will take place to repair the road surface and clear fuel spillages. It is anticipated the motorway will not open until tomorrow at the earliest, however we will endeavour to keep the public informed as soon as we can.

Diversions have been put into place and traffic is being diverted via A38 through North Petherton. Traffic is already heavy and will continue to remain so, Motorists are asked to anticipate delays.

Anyone who has still failed to make contact with loved ones or friends is asked to please call 0800 092 0410. If you genuinely fear for the welfare of a friend or loved one, and you fear they may be injured.

Before you call this number, please make all attempts to contact them via mobile phones or via friends, family or by any other usual measures.

Approximately 400 calls have been taken via this number and 250 dropped as a result of the recorded message advising this is not for routine updates.

Assistant chief constable Anthony Bangham said the motorway accident was "just about as big as it gets".

He said some members of the public had shown "real bravery" in arriving quickly on the scene and trying to help others, thanking those who had taken actions themselves.

"The intensity of the fire - it was a fireball on the carriageway - made it incredibly difficult for people to approach," he said. "People did their very best."

A mixture of heavy goods vehicles and light vehicles were involved, and a number were in close contact, burnt and unrecognisable.

Bangham described it as a "real mash of many, many vehicles", and said it was believed that some people were still trapped inside.

He added: "The goods vehicles were well alight and have been very significantly burnt."

Police have responded to suggestions that smoke from nearby fireworks displays may have worsened the foggy conditions.

They could not say whether the fireworks display at nearby Bridgwater Guy Fawkes carnival might have been a factor, but assistant chief constable Anthony Bangham said it was "certainly something we'll be looking at closely".

There's a number of factors that came into play. It was dark - it was about 8.25pm - it was particularly poor weather last night, we had fog banks on the motorway and we also had wet surface issues.

"We had, in particular, ground water in the Bridgwater area which we were dealing with. "There were also other factors coming into play: there were events going on in the evening and of course we need to have a very close look at what was going on in the area that may have caused some sort of distraction.

Aerial video courtesy of Channel 4 News shows the devastation caused by the fireball which engulfed vehicles at the centre of the 34 car pile-up.

The video shows that three of six trucks involved have been incinerated in the explosion while the charred remains of other vehicles are strewn across the northbound carriageway between junctions 25 and 26.

Elsewhere, cars can be seen caught under the trucks or pushed into the barrier area through the force of the crash.

Taunton rugby club said it was not prepared to comment on speculation that a fireworks display at the nearby rugby club may have contributed to the fog.

Oli Massingham said: "The only thing I will say is that the firework display started at 8pm and finished at 8.15pm."

Transport Secretary Justine Greening has expressed sympathy with the families of those affected by the tragedy and thanked rescue rescue workers and emergency staff who worked throughout the night to help the injured.

People living in the communities close to where last night's motorway accident happened are struggling to come to terms with the devastation today.

Josie Gallimore, 60, and husband Brian, 61, live near the accident scene in a cottage in Hyde Lane.

They learned of the devastating accident from neighbours and walked the few minutes to Hyde Lane bridge from their home.

The bridge overlooks the motorway and gave them a clear view of the crash scene involving dozens of mangled vehicles. Mrs Gallimore said:

It was about 11.30pm and there were helicopters and fire engines and a lot of noise We didn't stay long because it was too disturbing. You could hear the cries of the little ones trapped in their cars. They had to remain in their cars with their families and apparently some were there for up to three and a half hours. We walked back home afterwards and we could hear the sirens going until about 2am. There were helicopters as well. I didn't sleep last night. I couldn't. It's a terrible tragedy.

The police have said there are still people unaccounted for who may be trapped in their vehicles since last night.

After visiting what he described as the "horrific" scene of the 34-vehicle pile-up, assistant chief constable Anthony Bangham said the rescue operation was "incredibly difficult".

We have had contact with a number of people who are concerned that their loved ones have not returned home. We just fear that certain vehicles may still have people trapped. The main thing is we support the families at this particular time

The police are advising motorists to avoid the M5 north of Taunton. The motorway remains closed in both directions between junctions 24 and 25 with the northbound carriageway expected to stay shut until tomorrow at the earliest.

There are also delays at junction 23.

A witness has described the moment he dodged flying debris from cars to help save a desperate mother carrying her baby and young child.

Tom Hammill, from Wells, Somerset, told the BBC:

The fog was so thick it was like driving into a tin of emulsion. ''It was a black sheet, you couldn't see anything. ''I'd slowed right down and had veered into the central reservation and I think that saved our lives. The thing that made me realise how bad it was, was you could hear the thud of cars hitting into lorries. One car overtook us going at about 60 or 70 miles an hour and just crashed straight into a lorry. ''One woman who was carrying a baby and child was desperate - she was screaming 'take my baby'. ''So I took her baby and carried it over the central reservation where I was met again by the mother who also had a toddler. ''While I was there a bumper flew off a car and zoomed over my head, I heard my girlfriend scream 'watch out'. Then I went back to my father, who was in the car with a broken leg.''

• This article was amended on 7 November 2011 to remove a reference to Bridgwater Carnival. The fireworks display near the site of the accident was at Taunton Rugby Football Club, not Bridgwater Carnival. No fireworks were set off at the carnival, which is more than 10 miles from Taunton, on Friday evening.