HONG KONG, Feb. 1 (Xinhua) -- Hong Kong Police bomb disposal experts on Thursday defused a second World War II bomb found at a construction site in Wan Chai after a 24-hour operation.

The bomb was discovered by workers at the construction site for Sha Tin-Central rail link on Wednesday morning. It was the second time within a week that an unexploded American bomb had been discovered at the same location.

Police sealed off the site and about 4,300 people around the site were evacuated after the discovery of the 900 pounds bomb.

Hong Kong police began burning off the explosives inside the device at around 8 a.m. local time on Thursday. Black smoke was seen billowing from the site, and the air was filled with the smell of explosives. After about four hours, the gunpowder in the bomb was burned up and the bomb was lifted by the crane.

Alick McWhirter, a police bomb disposal officer, told reporters on Thursday that the operation was dirty, difficult and dangerous.

"Because of the rain yesterday, the working conditions were not good. And it was extremely difficult for us to be able to access the bomb due to the location. Because of the nature of the firing mechanism and the fuses -- one of which we couldn't even see -- it was extremely dangerous for the officers engaging in the disposal operation," McWhirter said.

"But we overcame all the difficulties and finally defused the bomb."

According to Hong Kong police, both of the bombs are believed to be dropped by American warplanes during Japan's occupation of Hong Kong between 1941 and 1945.

In 2014, Hong Kong found a World War II bomb in the downtown area.