The disposal took place at a harborfront construction site in Wan Chai, one of Hong Kong's busiest commercial areas and the site of the city's third-tallest building, the Central Plaza skyscraper.
The entire district was sealed off after construction workers discovered the 992-pound bomb and disposal workers were up all night defusing it so business could resume Thursday morning.
"Bomb disposal operations are dirty, difficult and dangerous. In this particular case, all three were true," bomb disposal officer Alick McWhirter told the South China Morning Post, adding that the disposal was no easy feat. It was done in pouring rain, with the bomb placed in a sensitive position. The team couldn't even see the fuse mechanism, McWhirter said.
Instead, the experts cut a large hole in the bomb and burned out the explosives. A crane then lifted the deactivated bomb away for permanent disposal. The entire operation lasted 50 hours in total.
"It was extremely dangerous for the officers engaged in the disposal operation," McWhirter said.
"We couldn't sleep. In such situations, the longer [the operation] takes, the more unstable [the bomb] is. That's why we had to work as quickly and as safely as possible," an exhausted officer who asked to remain anonymous told SCMP on Thursday.
The device was an AN-M65, built in the US and sold to British forces who dropped it on Imperial Japanese ships moored at the city. Japanese forces captured the city from the British in December 1941, beginning an occupation of Hong Kong that would last until the end of the war in August 1945.
Approximately 7,000 were killed in the battle, 4,000 of whom were Hong Kong civilians. An additional 10,000 civilians were executed by the infamously brutal Imperial Japanese over the course of the occupation.
Historian Jason Wordie told AFP that post-war land reclamation activities had likely moved the bomb inland, as it probably had fallen in the water during the war. "Hong Kong's main value during the Japanese occupation was its ship repairing facilities, so putting those out of action was harming the Japanese war effort," he said.
He added that there were likely "stacks more" Allied bombs in reclaimed lands waiting to be uncovered. Another bomb was found and defused in Wan Chai on Sunday.
In 2014, a one-ton shell was found in the city and defused without incident.