The Hong Kong Airport Authority and two airlines said on Friday they had received a warning from Taiwan authorities regarding a possible bomb aboard a Cathay Pacific or Dragonair flight arriving from mainland China in the next two days.
The warning comes amid heightened security concerns in China following suicide bombings and stabbings that have been blamed on Uighur separatists and after authorities in the restive region of Xinjiang region sentenced nine people to death on Thursday for "violent terrorism".
It also comes just two days after more than 180,000 people gathered for a candlelight vigil in Hong Kong to mark the bloody crackdown on pro-democracy protesters 25 years ago in Beijing's Tiananmen Square.
"We are aware of a threat message with reference to our flights from mainland China to Hong Kong as shared by the Taiwan authorities," a spokesperson for Cathay Pacific and its unit Dragonair said.
"We will continue to work closely with the relevant authorities and have reminded our frontline teams to remain vigilant as usual."
The Hong Kong Airport authority said flight operations at the airport were normal on Friday.
Spokespeople for the Hong Kong Airport Authority, Taiwan's Civil Aeronautics Administration and budget carrier HK Express confirmed the warning and said they were taking steps to maintain the safety of their passengers.
The Hong Kong bomb warning involves a woman who may be planning to board a Dragonair or Cathay Pacific flight to Hong Kong on Friday or Saturday, the South China Morning Post reported, citing a Taiwanese airport police source and intelligence from Taiwan's National Security Bureau.
The report did not explain the woman's motivations and did not tie her to any separatist groups.
China is in the midst of a nationwide crackdown on militant separatists that has resulted in hundreds of people being detained and 81 people from Xinjiang, home to the large Muslim Uighur minority, being sentenced for involvement in "terrorist organisations" and crimes ranging from arson to homicide.
The threat comes amid increasing tensions between mainland China and Hong Kong, which returned to Chinese rule in 1997 but remains a free-wheeling, capitalist hub.
Hong Kong residents have increasingly taken to the streets to protest against perceived meddling by China in the city's affairs.
This year is a sensitive one for the Asian financial centre, with debate over constitutional reform looming and pro-democracy activists planning to hold mass protests in July to demand the right to choose their own candidates for a poll in 2017 to elect the next Hong Kong leader.
Details of the threat had been sent to Hong Kong and mainland Chinese authorities, director of Taiwan's Civil Aeronautics Administration air transport division Chen Jau-yuh said.