Hong Kong/Singapore: Health authorities in densely-populated Hong Kong and Singapore have warned that Covid-19 cases are spiking, as a resurgent wave spreads through Asia.

The virus' activity in Hong Kong is now "quite high," Albert Au, head of the Communicable Disease Branch of the city's Center for Health Protection, told the media this week. The percentage of respiratory samples testing Covid-positive in Hong Kong recently reached its highest in a year, Au added.

The centre's data showed that severe cases reached their highest level in about a year, at 31, in the week through 3 May. Also, the resurgence has yet to match the infection peaks of the previous two years. The rising viral load found in sewage water and Covid-related medical consultations and hospitalisations suggest the virus is actively spreading in the city of over 7 million people.

Meanwhile in Singapore, in its first update on infection numbers in almost a year, this month, the city’s state health ministry estimated the number of Covid-19 cases jumped 28 per cent to 14,200 in the week through May 3 from the previous seven days, while daily hospitalisation rose around 30 per cent.

Experts predict that the increase in cases may have occurred due to factors including waning population immunity, but Singapore's health ministry said there is no indication that the circulating variants are more transmissible.

The hike in two of Asia’s most significant cities comes as Covid-19 has risen across the region in the past few months, with waves of the now-endemic disease swelling periodically. Health authorities have called on people to update their vaccinations, reminding high-risk individuals to get booster shots.

Unlike other respiratory pathogens, Covid-19’s comeback as the northern hemisphere enters summer shows the virus can still sicken a large swath of the population even when the weather is hot.