An unexploded World War II bomb has been safely detonated at sea after being transported through the eerily empty streets of English port city Plymouth where it was found.

In what prompted one of the largest evacuations in the UK since the war, a military convoy carried the Nazi-era explosive from a residential backyard in the city to Plymouth’s shoreline.

After a huge security operation, about 10,000 people were told they could return home.

“We have been notified by the military that the operation has been a success and the bomb has been removed,” Plymouth City Council said.

Tweet from @ChSupt_IanDS

Plymouth, a famous naval port 385km southwest of London, was targeted by Germany’s Luftwaffe during World War II, particularly during the Blitz in 1940 and 1941.

More than 2500 high explosive bombs were dropped on the city during the war, with many missing their intended target and falling on residential areas.

More than 1100 civilians in the city died during the air raids.

The bomb was believed to weigh about 500kg, according to the UK Ministry of Defence.

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The main train line into the city was closed as the convoy travelled through the cordon, while ferries were suspended and buses diverted.

Schools and nurseries also closed to allow the operation to take place, while all businesses within the cordon were told to evacuate.

Since the end of the World War II, unexploded ordnance have been regularly found across the UK.

An estimated 10 per cent of German bombs that were dropped during the war did not go off, leaving many towns and cities in the UK littered with dangerous explosives.

“I think it is fair to say that the last few days will go down in history for Plymouth,” said Tudor Evans, the leader of Plymouth City Council.

—AAP