Around 20,000 people are being evacuated from their homes in the German city of Cologne as experts try to defuse three Second World War bombs.

Axar.az reports, citing Sky News, it's the biggest ever post-war evacuation in the city and follows the discovery of two 1,000kg and one 500kg American devices on Monday.

The size of the bombs means that a 1,000m danger zone has to be cordoned off and closed.

Officials have been going door to door checking that businesses and houses in Cologne's Old Town and Deutz areas are empty.

Nine schools, 58 hotels, a hospital, the main city hall and the area close to Cologne's famous UNESCO-listed cathedral are among the numerous places temporarily off limits.

Two shelters have been set up for those affected.

It's reported that 1.5 million bombs were dropped on Cologne during the Second World War.

Experts estimate around 20% didn't fully detonate.

Some of these so-called "duds" still lie unexploded beneath the streets and have prompted numerous evacuations over the years.