THESSALONIKI, Greece – A massive evacuation has begun in the northern Greek city of Thessaloniki so experts can defuse a 500-pound unexploded World War II bomb.

Police went house-to-house Sunday morning, ringing bells and knocking on doors to remind people living within a 1.9-kilometre (1.18-mile) radius of the bomb site to leave their homes. Most were leaving in their cars, but some were being transported by bus to schools, sports halls and cultural centres elsewhere in the city, where they can get food and shelter.

Authorities believe about 75,000 people will be evacuated, most from the western suburb of Kordelio. A state of emergency has been declared in the area involved and about 1,000 police and 300 volunteers are helping in the evacuation. Trains have been halted in the area and church services cancelled.

The bomb, dropped during an air raid in the 1940s, was found earlier this month during work to expand storage tanks under a gas station. Defusing it is expected to take about six hours.

“It’s the first time something like this is happening in Greece,” Thessaloniki Deputy Governor Voula Patoulidou told The Associated Press.