The massive device was found by the Army's 33 Engineer Regiment's Ordnance Disposal team on Monday, during a three-week survey of Studland Beach.

The controlled explosion carried out on Wednesday could be heard across the bay in Bournemouth, according to witnesses.

The beach was the site of rehearsals for the D-Day landings and munitions from the era still surface.

We didn't know what it was so we went outside and all the car alarms in the street were going off Mathew Waite

The National Trust, which owns the beach, had asked the Ordnance Disposal team to survey the beach to find any remaining bombs.

David Hodd, of the trust, said new hi-tech equipment meant that munitions, which had been buried deep in the sand, could now be uncovered.

"The bomb, which the disposal team think was American, was discovered 8ft (2.4m) down," said Mr Hodd.

"The explosion was quite impressive - there was a puff of smoke about 100ft (30.4m) in the air and the ground shook a bit."

'Flat shook'

The area's history means that such controlled explosions are quite common.

But Mr Hodd said a man who had been working for the trust for 40 years described it as the largest blast he had seen.

Mathew Waite, 20, a student in Bournemouth, said the windows in his flat shook from the force of the blast.