By Tyrone Siu and Jessie Pang

HONG KONG, Jan 26 (Reuters) - A group of protesters set alight on Sunday the lobby of a newly built residential building in Hong Kong that authorities planned to use as a quarantine facility, as public fears in the financial hub about the coronavirus outbreak intensified.

A Reuters witness saw several masked protesters, clad in black, rush into the public housing block in Hong Kong's Fanling district near to the border with China, and set alight a Molotov cocktail before running out. Black smoke could be seen pouring out of the building to the sound of fire alarms. Windows were smashed.

Earlier in the afternoon, hundreds of regular Hong Kong citizens had blocked roads leading to the building with bricks and other debris, as anger grew towards government plans to convert the building into a quarantine zone as the number of confirmed cases in the city climbed to six on Sunday.

"We are dissatisfied with the government selecting this housing estate as a (quarantine) separation village as it's very close to a residential area and a primary school," said a 28-year-old resident surnamed Tsang.

Public calls have also grown for the Hong Kong government to block the financial hub's border with mainland China to further minimise the risk of infection.

Earlier on Sunday, Hong Kong authorities said they would convert "Fai Ming Estate, an unoccupied public estate in Fanling, into temporary flats for quarantine and observation of close contact persons without symptoms if needed."

Health authorities in the afternoon said 107 people were now under quarantine, and there were 77 suspected cases.

The ability of the new coronavirus to spread is strengthening and infections could continue to rise, China's National Health Commission said on Sunday, with nearly 2,000 people in China infected and 56 killed by the disease.

A handful of cases have been reported outside China, including in Thailand, Australia, the United States and France, with health authorities around the world racing to prevent a pandemic. (Additional reporting by Felix Tam; Writing by James Pomfret; Editing by Toby Chopra)