A controlled explosion has been carried out on a 500lb Second World War bomb which was dislodged from the seabed by dredging work for the next generation of Royal Navy aircraft carriers.

Disruption was caused to cross-Channel ferries as a 500-metre cordon was placed around the unexploded bomb found in Portsmouth Harbour, Hampshire.

As the ordnance was towed out of the harbour and into the Solent, the nearby Gunwharf Quays shopping centre as well as the Portsmouth Historic Dockyard - home to HMS Victory and the Mary Rose Museum - were evacuated as a precaution, along with residential areas in Old Portsmouth.

The bomb was towed to an area east of the Isle of Wight where a controlled explosion was carried out by the Royal Navy's Fleet Diving Squadron at 4pm.

An area of restricted air space was also established until the bomb had been destroyed.

Its discovery came after a 1,100lb German bomb was found at the end of September by the dredging barge, which caused the nearby Gunwharf Quays retail and leisure centre to be evacuated. A torpedo was also found earlier in September.

Commander Del McKnight, the squadron's commanding officer, said: "Last year we had more than 450 call-outs around the UK so this is really business as usual for us.

"We've had more call-outs to Portsmouth than we would usually see because of the extent of the dredging works being done to make way for HMS Queen Elizabeth, but we have teams on standby at 10 minutes notice around the UK ready to deal with these things."

A Royal Navy spokesman said: "The device was found by a dredging barge carrying out work in the harbour before the arrival of HMS Queen Elizabeth - the Navy's new 65,000-tonne aircraft carrier - into the naval base next spring."