Hong Kong medical authorities said Sunday a third case of A/H1N1 flu infection has been confirmed in the city.

The confirmed patient, a 23-year-old male student studying in the United States, arrived in Hong Kong late Saturday aboard Cathay Pacific flight CX 831, said Thomas Tsang, controller of the Center for Health Protection(CHP).

The man, who was a native of China's southern province of Guangdong, was taken to hospital directly from the airport after he was found having a fever when passing thermal scanning, Tsang said at a press briefing Sunday afternoon.

The man started coughing since May 14, a reason for which he has been wearing a facial mask on the plane.

The CHP chief urged passengers traveling on the same flight within three rows of distance to the patient, who seated in Row 60,to contact the center to see if quarantine measures were needed.

"Hong Kong students in North America should stay where they are for medical treatment rather than board an airplane if they develop flu-like symptoms," said Gabriel Leung, under secretary for Food and Health of the HKSAR government.

He pledged Hong Kong would maintain tight control at border points as the virus continues to spread.

Hong Kong reported the first confirmed A/H1N1 flu case on May 1,which involved a 25-year-old Mexican man. It triggered higher flu alert level in Hong Kong and led to quarantine of hundreds including air passengers, hotel guests, among others. All those put in quarantine, including the patient, have been discharged.

The second confirmed case surfaced on May 13, when a local resident traveling back from the United States tested positive for the virus.

Editor: Yan