A major incident was declared at Didcot power plant at around 4 p.m. local time (1600 UTC) on Tuesday, after a power station collapsed while workers were preparing the 10-story building for demolition.

The former coal- and oil-fueled plant, which lies around 70 miles (113 kilometers) west of London, closed in 2013 and had three large cooling towers that were demolished in 2014.

Nathan Travis, deputy chief fire officer of Oxfordshire Fire & Rescue Service, told reporters at the scene that there were no explosives on site at the time of the incident.

Dogs were carrying out a "systematic search of the rubble" in an effort to find three people who were believed trapped under the debris, Travis said.

Cause unknown

Six ambulances, two air ambulances and a hazardous response team were sent to the site on Tuesday afternoon, with several casualties taken to hospital in nearby Oxford. Around 50 people were also treated at the scene for dust inhalation.

Fire services said although dust from the collapse covered a large area, there were no hazardous materials found within the building.

Local witnesses in Oxfordshire told British media that they had heard a loud explosion.

"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," David Cooke, whose company Thames Cryogenics has a building overlooking Didcot power station, told AFP.

"It totally obscured the towers and must have drifted across the roads and main rail line. What's left looks a tangled mess."

The cause of the collapse, and the identities of the dead and injured, has not yet been made clear.

ksb/cmk (AFP, AP)