Health Secretary Lo Chung-mau on Saturday said the fatal oxygen blunder at Caritas Medical Centre this week involved a switch control problem, and its cause will be thoroughly investigated.

He was commenting on a 79-year-old patient who died after his oxygen cylinder was left switched off as he was being transferred from a ward to intensive care. He suffered cardiopulmonary failure and died about an hour and a half later.

Speaking to reporters after attending an event, Lo said opening an oxygen cylinder does not require highly skilled practitioners.

"Medical incidents are something that none of us want to see, but we understand that they could happen. This incident only involves a switch control issue. It doesn't involve any high-tech medical procedures."

Asked whether a spike of flu cases on the mainland will affect the SAR, Lo said every place is facing the threat of winter influenza. He called on travellers to maintain personal hygiene when travelling abroad.

Lo said more than 1.4 million people have been vaccinated against the flu so far, adding that the government will ensure the supply of flu jabs.