Singapore's health ministry on Sunday "strongly" advised unvaccinated individuals, especially the elderly, to stay home as much as possible over the next few weeks, citing heightened concerns about the risk of community spread of COVID-19.

The country reported 88 new locally-transmitted coronavirus cases on Sunday, the highest daily toll since August last year, driven by growing clusters of infections linked to karaoke bars and a fishery port.

Though Singapore's daily cases are only a fraction of the number being reported among its Southeast Asian neighbours, the jump in infections is a setback for the Asian business hub, which has successfully contained its earlier outbreaks. On July 10, it had reported no new cases.

As a precaution, authorities on Sunday shut fresh fish and seafood stalls in markets across the city-state as it tested fishmongers for COVID-19.

"We are concerned that there remain cryptic transmission chains which might continue to spread within our community. The porous nature of wet markets makes contact tracing and isolation less straightforward," the health ministry said in a statement late on Sunday.

About 73% of Singapore's 5.7 million population has received the first dose of a COVID-10 vaccine, but the government is pushing to get more of the elderly vaccinated, as those above 70 years of age have the lowest takeup rates at about 71%.

The rising cases prompted the city-state to tighten some restrictions on social gatherings from Monday just a week after easing them. However, it has more lenient rules for those who have been vaccinated.

As Singapore's vaccination rates rise and it prepares to live with the virus, the government has said it will look beyond case numbers at severity of illnesses to decide on further virus measures.

Of the 243 people with COVID-19 currently in hospital, five had serious illness requiring oxygen supplementation, and one was in a critical condition in the intensive care unit.