UPDATE: 3.55pm

A South Wales Fire and Rescue Service spokesman confirmed the firefighters were injured while en-route to another incindent in the Torfaen area and that one firefighter remains in hospital.

He said that colleagues from the South Wales Fire and Rescue Service worked with colleagues from the Welsh Ambulance Service and Gwent Police to release two other firefighters from the vehicle.

He added: "as is standard practice Gwent Police is now investigating the circumstances of the collision and the service is co-operating fully with the investigation.

"No other details on cause of collision are available at this time and the thoughts of the South Wales Fire and Rescue Service are with the firefighters involved and families."

The firefighters involved are retained, part-time crew.

UPDATE: 3.14pm

Sandra Rumble, who was visiting her daughter-in-law in Blaenavon, said she was driving near the scene at about 11.30 and heard the sirens and saw the air ambulance helicopter flying over.

She added: "I saw the rapid response vehicles gathering on the road but I couldn't see a fire engine, which worried me as I think it must have gone over the mountain near the Cordell Pub.

"The air ambulance left about 12.35pm towards Cardiff.

"I believe that another person was taken to Nevill Hall and at that time another was still trapped.

"There has been constant rescue vehicles passing and the mountain rescue helicopter. "We are just waiting for news as we know two people who are Blaenavon fire fighters and we just hope they're not involved."

UPDATE: 2.35pm

The firefighter taken by air ambulance to the University Hospital of Wales was complaining of neck pain and had a possible broken leg, a spokesman for the Welsh Ambulance Service NHS Trust confirmed.

Three firefighters were taken to Nevill Hall hospital with back injuries and a fifth firefighter was treated at the scene.

UPDATE: 2.00pm

A resident whose house is in the cordon told us: "It all kicked off about midday when I heard lots of sirens. I tried taking my dog for a walk but found the road closed.

"I spoke to people who said it was a serious accident involving an overturned fire engine.

"Since then there has been air ambulance, fire engines and police constantly coming and going."

UPDATE: 1.31pm

The fire service said the crew from Blaenavon were responding to an accident when the crash happened.

The injured firefighters have been taken to the University Hospital of Wales in Cardiff and Nevill Hall Hospital in Abergavenny.

Diversions will be in place for 'several hours' while police carry out enquiries.

UPDATE: 1.03pm

Police are diverting traffic after the fire engine crash earlier today on the Blaenavon to Govilon Road (Keepers Road).

UPDATE: 1.00pm

One firefighter is seriously injured and has been taken by air ambulance to hospital.

Four other crew had minor injuries.

UPDATE: 12.45pm

AN air ambulance has been scrambled to take casualties from the scene of the fire engine crash.

An eyewitness said the Wales Air Ambulance landed and took off and that an RAF search and rescue helicopter is also hovering at the scene.

The crash happened around an hour and a half ago.

UPDATE: 11.30pm

AN OVERTURNED fire engine has closed the Abergavenny Road (B4246) in both directions between Blaenavon and the Govilon junction.

Heavy lifting equipment is en-route to the scene.