Thousands of people in central Berlin were ordered to evacuate on Thursday evening after an unexploded World War II bomb was discovered in the Spree River.

Police set up a security perimeter of 500 meters in a densely populated area in the center of the German capital.

Officers went door-to-door within the security perimeter to inform residents of the evacuation order.

Around 10,000 people were told to leave their homes, police said.

Berlin's Tagespiegel newspaper reported long lines at an emergency overnight shelter at the town hall in the Berlin Mitte district, with hundreds of people reported waiting to register for a place to spend the night. Another shelter at a nearby school was opened shortly after midnight to accommodate the high number of people. 

The neighborhood is also home to several embassies and city administration offices. 

Bomb declared safe

Early Friday, authorities announced that a World War II bomb discovered in the Spree River in Berlin's central Mitte district does not need to be defused.

"We can give the all-clear," a Berlin police spokesman told dpa. "There is no longer any danger. The bomb does not need to be defused." 

Authorities said the bomb was discovered during construction work near the Fischerinsel in central Berlin. Checking for unexploded ordnance from World War II is common practice in German cities ahead of large construction projects.

The bomb was found under four meters of water, and was covered in silt and slime, which complicated the operation, police said. 

Residents were due to be allowed to return to their homes on Friday morning after police gave the "all-clear," a spokesperson said.

Ship traffic on the Spree, which runs through the city, had been halted overnight. Streets were also closed and service on subway line 2 was suspended.

Thursday's bomb disposal evacuation was one of the largest in Berlin in recent years.

Another bomb to be defused in Spandau

Meanwhile, in the Spandau district of Berlin, a 100-kilogram wartime bomb that was discovered on Wednesday is expected to be defused on Friday.

A safety zone has been set up around the site, and a local gym has been opened as an emergency shelter for evacuees.

Since the bomb did not pose an immediate threat, police decided to defuse it at a later time. The site has been cordoned off, and according to the police, it has been guarded by officers since then.

Approximately 12,400 people in the district have been evacuated.

Edited by: Karl Sexton, Roshni Majumdar