The victims were working for a building contractor carrying out work on an extension at offshore specialist Claxton Engineering’s yard.

It is believed the men were working below ground on foundations when tonnes of steelwork collapsed on top of them.

Planning permission for the extension was only granted in late December on the £250,000 contract which involves construction of two steel test chambers with a brick construction compressor house/controllers room.

The dead men were named locally as Dan Hazelton, 30 and his brother Tom Hazelton, 26, and Peter Johnson, 42, all from Stanton, near Bury St Edmunds, Suffolk, plus Adam Taylor, 28, who lived close by.

The name of the main contractor has not been confirmed by the authorities.

A statement released by Claxton said: “Claxton Engineering Services Limited can confirm that an accident occurred at its premises in North River Road, Great Yarmouth where construction work on a new facility is being carried out by external contractors.

“We are also able to confirm that four men have tragically lost their lives in this incident which is now being investigated by the Norfolk Constabulary and the Health and Safety Executive. The company is fully co-operating with the investigation.

“Everybody at Claxton is deeply saddened by what has occurred today and the company’s thoughts and sympathy are with the families of the four men.”

Police, ambulances and nine fire crews including urban search and rescue units attended but the men died at the scene.

A joint investigation has been launched by Norfolk and Suffolk Major Investigation Team and the Health and Safety Executive (HSE).

Det Chief Insp Neil Luckett from the major investigation team said: “This is a tragic event and we will be working closely with the HSE to establish the full circumstances surrounding the incident. This may be a lengthy process. Our thoughts are with the families of the men who died.”