The news comes as Marine Department officials investigate reports of another attack last week, hours after two ships were fired on south of Hainan Island.

Crew aboard the Danish-registered freighter Lion fired two rocket flares to scare off pirates who hit their ship with 15 bullets.

The 1,300-tonne ship was sailing from Pusan, in South Korea, to Singapore when it was attacked about 400 kilometres south of Hongkong.

A Security Branch spokesman said: ''Obviously we're concerned, but as yet there is no evidence of sustained attacks in the region.

''We have an obligation under international maritime law to respond to distress calls and notify other authorities of [pirate] incidents that come to our attention.

''We do not have any role outside, or the facilities, for any role outside of that.'' Branch officials are examining what role the territory can play as part of a ''watching-brief'' on piracy following raids last week.

Pirates aboard a fishing boat aborted a third attack when they were repeatedly buzzed by a Royal Hongkong Auxiliary Air Force aircraft, responding to a distress call received by the Marine Department.

The success of the RHKAAF response, considered a one-off, has blurred the lines between their neutral rescue role and semi-military, anti-piracy action.

''What if the 'pirates' had actually been public security bureau officers, or had fired shots?'' one Government source asked.

''The auxiliary's action has forced us to think along those lines.'' Senior sources in the Government said ''dicey political questions'' would have to be tackled if Hongkong was to take any such action in the future, given sensibilities and disputed territories off the coast of southern China.

The Security Branch spokesman said the RHKAAF, as a neutral civilian organisation, should not take unnecessary risks.