Police established a six-day security perimeter around the Zaluzi plant about 100 kilometres (60 miles) northwest of Prague after workers had found the ordnance at a remote part of the factory's site on August 21.

They ordered hundreds of people to leave their homes, while the factory run by Polish petrol giant Orlen was shut down.

"The detonation of the bomb was successful. The blast occurred at 12:13 (1013 GMT)," the fire brigade said on X, posting drone images from the site.

"We are conducting a thorough check of the site. The initial visual search suggests there are no major visible damages in the neighbourhood," it added.

The firefighters isolated the bomb with sandbags before the blast.

The 250-kilogramme (550-pound) British aerial bomb was equipped with a unique chemical trigger to delay its explosion, which police said made it particularly dangerous.

"The danger and rarity of this discovery lies in the triggering mechanism that can be set for up to 144 hours, or six days," a police statement said last week.

Besides the 1.5-square-kilometre perimeter, the Czech police also ordered 600 people to evacuate.

The factory, which served the Nazi war effort during the German occupation of then Czechoslovakia, was the target of Allied bombings in 1944.