Students wearing face masks run for shelter during a sudden but brief heavy downpour in Hong Kong on July 8, 2020. (ANTHONY WALLACE / AFP)

Hong Kong's number of new local COVID-19 infections that can’t be traced suggests that hidden chains of transmission have been circulating in the city for some time as social distancing measures were eased and people returned to work and normal life.

Hong Kong reported 19 new infections in the community on Wednesday with six of unknown origin -   the most since April 1. This follows the disclosure of nine new locally-contracted cases on Tuesday, five of unknown origin.

The resurgence of cases in HK, termed “the third wave” by officials, comes two weeks after the government’s latest easing of social-distancing restrictions

READ MORE: HK's new COVID-19 cases jump by 24, 19 locally transmitted

An additional six infections were detected by authorities on Wednesday night, reported HK01 on Thursday morning, suggesting that the spread is continuing.

The number of new local infections that can’t be traced suggests that hidden chains of transmission have been circulating in the city for some time as social distancing measures were eased and people returned to work and normal life. Hong Kong had successfully quelled two waves of infection in February and April and its total outbreak numbers only 1,323 cases.

The virus is flaring again across the Asian region, a reminder that the pandemic is far from over, even in places with the best containment track records. Australia’s second-largest city, Melbourne, re-entered virus lockdown this week as cases surged in Victoria state, while Japan continues to find about a hundred new infections daily in its capital of Tokyo. In Beijing, schools remain closed to halt a new outbreak, which has largely been contained.

The resurgence of cases in Hong Kong, termed “the third wave” by officials, comes two weeks after the government’s latest easing of social-distancing restrictions. Several cases were linked to renewed traffic to restaurants, as people remove their masks to eat and drink, said health officials.

READ MORE: HK 'facing community outbreak' as local COVID-19 cases jump

At least 13 educational institutions have suspended classes and visits to elderly care centers are being limited after cases were found in these places.

“We are worried that there may be a major community outbreak because of so many unknown sources,” said Chuang Shuk-kwan, an official with the Department of Health at a Wednesday briefing. Chuang urged a re-tightening of social distancing measures.

“Tracing will be difficult. We are very worried. Seeing the experience from overseas, this kind of situation can turn into a very serious outbreak,” she said.