Hong Kong authorities have evacuated thousands of residents over a bomb left over from World War II that was discovered at a construction site. Police said the bomb – found on Friday – weighed about 450 kilograms (1,000 pounds), adding that they believed it remained “fully functional” and could have caused mass casualties if mishandled.

Police had said that a total of 6,000 residents needed to be removed from 18 buildings in the city’s Quarry Bay neighborhood.

In the early hours of Saturday, they said evacuations were complete, noting that more than 2,800 residents left with police assistance.

The bomb disposal operation has begun, and was expected to take 12 hours, police said.

Hong Kong was an early target in what would become a full-blown Asian campaign for imperial Japan during the Second World War.

The city saw fierce fighting between Japanese and Allied forces during wartime, and hikers and construction workers still occasionally discover unexploded bombs in the territory.

In 2018, a total of three US-made bombs were discovered in Hong Kong’s Wan Chai district.

Police said the unexploded ordnance unearthed on Friday was of the same type as the ones found in 2018.