One person has been killed, three are missing and five in hospital after a building collapsed at Didcot Power Station, Thames Valley fire service has said.
A major incident was declared after reports of a loud explosion at the site in south Oxfordshire around 4pm.
A Hazardous Area Response Team, six ambulances and two air ambulances have been sent to the scene, South Central Ambulance Service said.
“We are describing it as a major incident,” an ambulance spokesman said.
A Oxford University Hospitals NHS Foundation Trust spokesman said “casualties” were being taken to the John Radcliffe Hospital.
The public has been asked to stay away from the hospital unless suffering “serious or life-threatening emergencies”.
There are reports the collapse was part of planned demolition work at the site.
A GMB union official told the Press Association: “We understand that workers were preparing two boilers for demolition in the coming weeks. This led to the collapse of a building.”
Didcot A, a disused oil and gas plant, is currently being demolished, but a natural gas plant, Didcot B, is still functioning on the site.
Pictures show a part of Didcot A has collapsed, with large chunks of debris scattered on the ground.
Mobile phone footage shows a huge amount of smoke rising from the station.
Rodney Rose, deputy leader of Oxfordshire County Council, told the Oxford Mail: “At the moment this is being treated as a collapsed building, not an explosion, but there was a bang.”
David Cooke, who works in a building next to Didcot station, said: “Our building shook and as we looked out of the window, the end of the main turbine hall collapsed in a huge pile of dust.
“It totally obscured the towers and must have drifted across the roads and main rail line. What”s left looks a tangled mess.”
Didcot A ceased operation in March 2013 after more than 40 years or generating power for area.
It was originally a coal-fired station, but was later converted so it could also generate power from natural gas.
A huge fire ripped through Didcot B in October 2014. No one was injured, but the blaze put half of the gas-fuelled plant – which supplies a million homes – out of action.