A prison in the south-eastern German city of Regensburg is set to be evacuated after an unexploded bomb from World War II was found near the site on Wednesday, police have said.

The 225-kilogram aerial bomb was found at 430 pm (1430 GMT) during work at a large construction site in the city's west.

The historical relic is set to be disarmed on Saturday, police said, with the main evacuation of nearby residents and prisoners due to be begin from 9 am.

Some 109 inmates will be forced to leave the prison as part of the operation, according to the local Mittelbayerische newspaper.

It is the fifth WWII bomb to be found on the building site so far, the newspaper said.