LONDON — (CNN) The discovery of an unexploded World War II bomb has brought a bustling area of east London to a standstill and forced scores of people from their homes.

The 250-kilogram (550-pound) device has lain undisturbed for the past 70 years but was uncovered Monday afternoon by contractors working at a construction site on Temple Street in Bethnal Green.

The device is believed to have been dropped over London during German bombing raids in the early 1940s but didn’t detonate, the UK Ministry of Defence said.

A specialist military bomb disposal team worked through the night to try to defuse the device and remained at the scene Tuesday morning.

Images provided by the ministry showed the rusty device firmly embedded in the dirt.

At least 150 people were evacuated from their homes overnight, a 200-meter exclusion zone has been set up and several roads have been closed.

“The operation is likely to last throughout the night,” a council spokesman said Monday evening. “We understand that this will cause inconvenience for a lot of residents. We urge residents to look at alternative places to stay for the night.”

A local school has been called into action as an emergency shelter for people who can’t go home, Tower Hamlets Council said.

Military bomb disposal experts from the Royal Logistics Corps detonated similar devices discovered in London’s Wembley and Bermondsey areas earlier this year.

Thousands of bombs were dropped on London during the Blitz, from September 1940 to May 1941. Rocket attacks on the capital followed as the war dragged on.

According to the Imperial War Museum, it’s estimated that more than 12,000 metric tons of bombs were dropped on London in total and nearly 30,000 civilians were killed by enemy action.

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