The largest unexploded World War Two bomb ever found in Poland has detonated during the defusing process, a Polish Navy spokesman said.

The chance the bomb – at the bottom of a Baltic Sea shipping canal – would detonate had been put at 50-50 and all the divers were unharmed.

About 750 residents had been evacuated near the port city of Swinoujscie.

The RAF dropped the Tallboy or “earthquake” bomb in a raid in 1945 which sank the German cruiser Lützow.

Swinoujscie was part of Germany and called Swinemunde at the time of the bombardment.

The shock of the latest detonation was reportedly felt in parts of the city and a video shows the blast throwing up a large column of water into the air.

The bomb was 6m (19ft) long and weighed 5.4 tonnes, nearly half of which was its explosives.

The bomb was embedded at a depth of 12m and only its nose was sticking out.

Naval forces used a remote-controlled device to try to “deflagrate” the bomb – a technique that if successful burns the explosive charge without causing a detonation, the BBC’s Adam Easton reports from Warsaw.

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“The deflagration process turned into detonation. The object can be considered neutralised, it will not pose any more threat to the Szczecin-Swinoujscie shipping channel,” said Lt Cmdr Grzegorz Lewandowski, spokesman for the Polish Navy’s 8th Coastal Defence Flotilla.

“All divers were outside the danger zone.”