The biggest World War II bomb ever found in Poland exploded under water on Tuesday as navy divers tried to defuse it.

More than 750 people had been evacuated from the area near the Piast Canal outside the town of Swinoujscie where the Tallboy bomb used by Britain’s RAF was found. It weighed nearly 5,400kg, including 2,400kg of explosive.

“The deflagration process turned into detonation. The object can be considered as neutralised, it will not pose any more threat,” Second-Lieutenant Grzegorz Lewandowski, the spokesman of the 8th Coastal Defence Flotilla, was quoted as saying by the PAP news agency.

“All mine divers were outside the danger zone.”

Swinoujscie contains a liquefied natural gas terminal but a spokesman for the town’s mayor told PAP no one was hurt and nothing had been damaged. The Piast Canal connects the Baltic Sea with the Oder river on Poland’s border with Germany.