Health officials on Tuesday warned that an extended flu season would continue for some time, with more outbreaks and serious cases.

The Centre for Health Protection urged the public to remain vigilant as Hong Kong has seen a rise in flu infections, with more than 500 adults suffering serious complications or dying since January. Most of them are over 65 or have chronic illnesses.

There have been 22 severe flu cases among children, including three deaths.

Dr Chuang Shuk-kwan, from the Centre for Health Protection, said health authorities were closely monitoring the situation.

"The predominant flu strain has shifted from H3 to H1, resulting in another wave of infections. We expect this wave to continue for a few weeks, but it's difficult to say exactly how long," she said.

"We are closely monitoring other regions of the world, as Hong Kong residents travel a lot. Influenza B is still circulating in some parts outside Hong Kong, so we cannot rule out the possibility of a further change in the flu strain."

Health authorities urged the public to seek medical attention if they experience flu-like symptoms.