A builder fell 13 metres after the roof collapsed in a new section of Watford FC's Vicarage Road stadium.

Emergency services closed Vicarage Road while paramedics rescued the trapped victim.

He has been taken to the Royal London Hospital by air ambulance.

The police said the man fell after the roof of the new facilities collapsed in the North East Corner of the stadium.

Police spokesman Natalie Dearman told the Watford Observer: "They were working on part of the roof, then that collapsed and the person fell."

One builder at the scene said some temporary scaffolding had collapsed. But the health and safety executive has now begun an investigation.

Cliff Webb, watch commander from Watford Fire Station, said: "We were called to a trapped person. He had fallen from height.

"He was in a difficult position to get to. We made sure it was safe for the paramedics and then we tried to get some spine boards through as quickly as possible.

"An air ambulance landed on the pitch and we carried him through the building works then on to the pitch.

"He'd fallen from a part of the new stand.

"He was conscious and breathing and had head and leg injuries and a possible pelvic fracture."

Jake Ashby, spokesman for the East of England Ambulance Service, said: "We received a call to say someone had fallen from height.

"He suffered serious injuries to his legs and an injury to his head though it's not confirmed how serious it is.

"After being treated at the scene, he was flown to Royal London Hospital in a serious condition."

Ben Girvan, 17, saw the emergency vehicles arriving.

He said: "I saw the helicopter taking people to hospital. Two ambulances turned into the hospital.

"There were five fire engines.

"A police officer said there was a structural issue with part of the stadium.

"The police officer said there were people stuck under the new part of the stadium."