Germany’s financial capital, Frankfurt, has been brought to a standstill after a 500-kilogram World War II-era bomb was discovered on a construction site, prompting a mass evacuation.

Authorities ordered some 16,500 residents living within a roughly 1km radius of the unexploded bomb to leave their homes before experts moved in to disable at least one of its two detonators.

The ordnance clearance service gave the all-clear on Sunday afternoon (local time).

“It went smoothly,” a spokesman said.

The bomb which had been dropped by the US Air Force during WW2 was uncovered 10 days ago near the European Central Bank headquarters.

Officials chose Sunday to defuse it in order to minimise potential disruption of the city, which acts as the country’s financial capital.

The evacuation area stretched from the bank to the Main River on the eastern side of the city.

On top of the general lockdown in the run-up to the bomb disposal, several train services were suspended, the city’s zoo had closed, ships remained docked at ports and a runway at Frankfurt airport was temporarily shut down.

Police combed the city on the morning the bomb was scheduled to be diffused, with loudspeaker trucks circulating the area, urging any stay-behinds to immediately evacuate.

Nursing home residents including about 25 coma, stroke and dementia patients were transported to other hospitals and all incoming vehicles were diverted away from the area.

Some tourists were taken by surprise.

“The war was so long ago, and now something like this happened,”  Delilah Ahmed was quoted as saying.

“And there’s a bomb. And it’s 2019 and they are still disposing, they’re putting out bombs. So it’s bit weird,” said her friend, Jasmin Ali.

Frankfurt’s fire services are well-versed in bomb disposal operations.

“We did it! The World War II bomb in the Ostend neighborhood has been defused by the ordnance disposal team. Roadblocks and evacuation zones have been lifted,” the city fire service tweeted on Sunday, shortly after the bomb had been defused.

In September 2017, 65,000 residents had to be evacuated so that a British “blockbuster” bomb weighing 1.8 tonnes could be removed.

German authorities estimate that around 15 per cent of the bombs dropped during WWII failed to explode, and more than 2000 tonnes of unexploded weaponry are found each year.

In the rush to rebuild after the war, Germans often just buried the munitions.

-with AAP