“The controlled explosion was successful,” the police tweeted shortly after 1 am (0000 GMT). The 50-kilogram phosphorous-filled unexploded bomb had been found and damaged during construction work.

The real danger was not so much from bomb fragments but from the phosphorus within the device. “Phosphorus reacts to oxygen,” a spokesperson for the state-level Explosive Ordnance Disposal Service said, adding that the resulting cloud is very toxic.

Firefighters were on hand with hoses to counteract the hazard.

About 2,000 people had to leave their homes in the danger zone, which had a radius of 300 metres.

Patients from a local hospital also had to be taken to alternative facilities in the district. The police had asked for windows to be kept shut throughout the city.

On Thursday another World War II bomb was defused in Leipizig, in eastern Germany. Up to 10,000 people had to leave their homes while the device was made safe.