Large areas of the city center of Cologne were closed off on Wednesday as experts defused three bombs left over from World War II, which ended 80 years ago.

The evacuation operation in Cologne, which has seen plenty of them over the years, was one of the largest to ever be carried out in the city since World War II, with some 20,000 people ordered to leave the affected area.

What do we know about the evacuation?

The process of defusing the bombs had to be delayed at one point because of a resident refusing to evacuate, according to a city spokesperson.

An individual living in the old town resisted orders to leave their apartment, with public order officials, police, and the fire department enforcing removal measures.

Kai Kulschewski, head of explosive ordnance disposal in the nearby city of Düsseldorf, who is coordinating the disposal, had earlier said everything was going to plan. He had added that the defusing operation had yet to begin as of the afternoon because not everyone had been evacuated yet. 

"We can only start when the last person is out," he said. 

Hotels, care homes evacuated

The evacuated area included the entire old part of the city, 58 hotels, three Rhine bridges, the town hall, the railway station in the district of Deutz, which lies across the Rhine from the city center, museums, a hospital and two care homes.

The city's major landmark, Cologne Cathedral, was, however, situated just outside the danger area.

Germany's national rail operator, Deutsche Bahn, had warned that many trains will be diverted or even canceled, and road traffic has was severely disrupted. 

The weapons — two 2000-pound (900-kilogram) bombs and one 1000-pound bomb, all manufactured in the US — were discovered in Deutz on Monday.

In a statement on its website, the City of Cologne said, "The evacuation is the largest such measure since the end of World War II. Everyone involved hopes that the defusal can be completed in the course of Wednesday."

Bomb defusals are nothing new in Cologne, as it was one of the major bombing targets for Allied forces during the Second World War.

Among other attacks, the British Royal Air Force targeted Cologne with its first "thousand-bomber raid" on a German city overnight to May 31, 1942, dropping 1,455 tons of bombs and destroying or damaging thousands of buildings.

Correction: An earlier version of this article had incorrectly listed the bombs as weighing 200 and 100 pounds

Edited by: Elizabeth Schumacher, Wesley Rahn