A British World War Two bomb has exploded while being made safe underwater by navy demolition specialists in north-west Poland.

The 5.4-ton Tallboy bomb was found in September 2019 beneath a waterway leading to the port of Szczecin during work to deepen the passage.

More than 750 people were evacuated for the sappers’ operation since it was located on the southern edge of the popular Baltic Sea resort of Swinoujscie, which like Szczecin was a busy Nazi Germany military port during the war.

Polish navy demolition experts were trying to neutralise it underwater through remote deflagration, which means burning out its explosives, but it went off in the process.

A navy spokesman, Lt Col Grzegorz Lewandowski, said that no-one was injured since all the sappers were at a safe distance from the blast, which was felt by local residents in Swinoujscie.

“The operation was carried out perfectly and safely and the bomb is safe now,” Lt Col Lewandowski said.

He noted it was the biggest ever such operation by sappers in Poland, where unexploded wartime bombs, missiles and grenades are still found.

The Tallboy bomb was designed by British aeronautical engineer Barnes Wallis and was used by the Royal Air Force to destroy large Nazi-controlled assets through underground shocks.

The one in Swinoujscie was probably used in April 1945 on the Nazi German battleship Luetzow. Experts do not know why it failed to explode at the time.