Hong Kong tightened social distancing measures on Thursday to combat a fresh coronavirus outbreak in a city that had largely managed to quash local transmissions in recent months.

Health officials have been rattled by a cluster of new infections that have suddenly spread through the tightly packed business hub of 7.5 million people. The city recorded 34 locally transmitted coronavirus cases on Thursday, the highest daily tally in more than three months.

"Now that the pandemic is coming back, I appeal to everyone to reduce outings, gatherings and dining together," health minister Sophia Chan told reporters. Authorities announced a reintroduction of limits to how many people can gather together, a repeat of measures taken earlier in the year that helped stifle the coronavirus outbreak.

A maximum of eight people can sit together at restaurants while bars, pubs and nightclubs are capped at four people per table. Catering businesses can only operate at 60 percent of their usual capacity. Gyms and karaoke lounges must have no more than 16 people in each room or facility.

Hong Kong was one of the first places to be struck by the coronavirus earlier this year after it burst out of central China. But authorities made impressive headway against the disease, helped by a population with previous experience of outbreaks who readily adopted facemasks and social distancing.

The city has recorded 1,365 cases of the disease since January, with seven deaths. However, the new outbreak shows the stubborn resilience of the coronavirus, even in a city with a strong record of stopping its spread. New infection clusters started to emerge in the past two days, including at an elderly care home that reported at least 32 cases.

At least 12 new infections in the last five days have been classified as unknown in origin, meaning authorities are struggling to work out how the disease is spreading in those instances. Last month, Hong Kong relaxed its social distancing rules to allow public gatherings of up to 50 people, reopen theme parks and scrap customer restrictions for restaurants.