Tourist arrivals fell nearly 40 per cent in August from the same time last year, Financial Secretary Paul Chan Mo-po posted on his blog on Sunday.
That drop is the biggest year-on-year monthly decline since 2003, during the severe acute respiratory syndrome (Sars) outbreak, and follows a 5 per cent drop in July, the South China Morning Post reported.
Hong Kong's pro-democracy protests, triggered by a controversial extradition bill, have entered their 14th week and shows no signs of easing.
Protesters have forced the airport to close for two straight days, set fires in the streets across the city, and trashed dozens of railway stations.
The damage to tourism has sent shock waves through local industries from catering to hotels and retail.
"We have suffered a huge blow from the protests," said Wong Ka-ngai, chairman of the Hong Kong Tour Guides General Union, which represents some 3,200 out of the 6,000 tour guides in the city.
Hotels are also struggling to stay afloat even with aggressive price cuts.
Occupancy rates across the city have plunged below 50 per cent, from over 90 per cent in the past, according to Yiu Si-wing, a legislator representing the tourism industry and the chairman of China Travel Service (HK).
Restaurants are also under pressure to attract customers. Greenland Spicy Crab in Tsim Sha Tsui, which is famous for the local seafood dish, cut prices by half in September for as many as 30 dishes.
( With inputs from IANS )