A shark was reportedly spotted cruising off Stanley yesterday, four days before the Dragon Boat festival races on Saturday.
The report has prompted the marine police and the Leisure and Cultural Services Department to step up patrols and order their frontline staff to stay alert.
The department manages 36 beaches in Hong Kong.
'According to our informant, it is a two-metre-long shark, grey in colour,' a police spokeswoman said.
The shark was first spotted in Tai Tam Bay, about one kilometre off Stanley Main Beach, at around 11.30am yesterday. The man who called in the sighting was alone on a rubber boat when he saw it.
He reported it to police on his mobile phone before returning to shore. 'He told our officers that he last saw it cruising about 50 metres off the beach, before swimming away,' the spokeswoman said.
Marine police launches were sent to check and a Government Flying Service helicopter was dispatched in the afternoon, but no shark was found.