HONG KONG - Bomb disposal officers in Hong Kong on Sunday (Jan 28) successfully defused a 450kg wartime bomb discovered a day earlier at a construction site in Wan Chai.

A construction worker made a report to police at 7.40am on Saturday, prompting the evacuation of 1,300 people. The bomb was discovered at a construction site for the Sha Tin-Central rail link, a 17km cross-harbour extension of the city's MTR network.

Several roads around the Hong Kong Convention and Exhibition Centre were closed from midnight on Saturday.

Ferry services were also suspended and at least half a dozen cross-harbour and island bus routes are affected during the bomb disposal operation, reported South China Morning Post.

At about 11am on Sunday, officers initiated the process of burning off the explosive material inside the device. A plume of smoke was seen coming from the work site.

The operation ended at around 1pm on Sunday, Chow Shek Kin, senior bomb disposal officer with the Explosive Ordinance Disposal Bureau, told reporters at the site on Sunday. Footage of the briefing was posted on the Hong Kong Police's Facebook page.

He added that the operation took longer than usual because of the size of the bomb.

Officers said the ANM-65 device, containing about 225kg of explosives, was dropped from the air by American bombers between 1941 and 1945.

The large cylindrical device, 140cm long and 45cm in diameter, was unearthed 15 m down in the soil.

The police had to defuse the bomb on site because front detonator is damaged and would pose a danger if it was moved.

"So that's why we're doing a lot of protective work to make sure the bomb is contained within the area," Chow told a press conference on Saturday.

"It could cause extensive damage. If the bomb explodes the force could affect the surrounding area within 200 metres, with fragments flying as far as 2,000 metres."

Those evacuated included residents and workers from nearby offices, the Hong Kong Convention and Exhibition Centre and nearby hotels, reported local media.

In January last year, a 220kg unexploded US wartime explosive was found at a construction site in Pok Fu Lam. The airdropped bomb - model AN-64 - contained about 120kg of TNT explosives.

In 2014 a 900kg ANM-65 unexploded American bomb was found at a construction site in Happy Valley.