One person is dead, five injured and three more are missing after a building collapsed at Didcot Power Station in Oxfordshire.
Nathan Travis, deputy chief officer for Oxfordshire Fire and Rescue, said five construction workers were in hospital following the collapse in the disused Didcot A section of the site around 4pm on Tuesday.
They were preparing two boilers for demolition in ten days time, a GMB union official said.
A major incident has been declared and casualties have been taken to John Radcliffe hospital in Oxford.
Oxford University Hospital Foundation Trust has asked people not to visit their emergency department for anything other than serious or life-threatening conditions.
Rodney Rose, deputy leader of Oxfordshire County Council, said he had been told there had been at least one death at the site.
He told the Oxford Mail: “I have been told there has been one fatality, but the rest is currently unknown.
“The fire service is there now and we are still trying to find out if this was a demolition.
“At the moment this is being treated as a collapsed building, not an explosion, but there was a bang.”
Authorities have confirmed a building on the defunct Didcot A part of the site had collapsed - leaving a large amound of debris on the ground.
But the chief fire officer, Dave Etheridge, said although the cause of the collapse is "unknown" it was not an "explosion" as has previously been reproted.
The fire service has advised people to stay indoors but said while dust from the collapse had covered a "considerable area" there were no hazardous materials in the building.
Adrian Redhead told The Independent: "There was this massive explosion, which sounded like a train coming off the tracks – it was that loud.
"Within 30 seconds emergency vehicles were all over the place. The amount of smoke and dust coming across was incredible."
South Central Ambulance Service confirmed they sent an air ambulance, three road ambulances, a rapid response vehicle and a hazardous area response team to the power station.
Residents nearby said they had heard a noise which sounded like "thunder" on Tuesday afternoon.
A road had been sealed off following the incident but police say it has been reopened.
One witness said there was "loads of dust" and "loads of emergency vehicles" at the scene of the explosion.
A spokeswoman for Thames Valley Police said they were "attempting to ascertain what happened" and would release further details in due course.
Local MP, Ed Vaisey tweeted to say he was "very concerned" about the explosion and was "praying for workers and their families".
The power station - which ceased coal production in 2013 - was due to be demolished in part after its cooling towers were knocked down in 2014.
A spokesman for the firm in charge of the demoliton, Coleman and Co, confirmed the building "was under demolition" but did not say whether there had been explosives on site at the time of the blast.
Didcot A opened in 1970 as a coal-fired power station but was later converted so it could also generate gas power.
According to RWE Npower - who manage the site - the total demolition of the site is due to be completed by the end of the year.
Additional reporting by PA
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