SINGAPORE - The next few days will be critical in Singapore's fight to stop the coronavirus from spreading, said Prime Minister Lee Hsien Loong in a Facebook post on Saturday.

Twelve days into the circuit breaker, there are some early signs that the stricter measures to reduce physical interaction among people are bringing cases down, Mr Lee said.

"But we are still worried about hidden cases circulating in our population, which are keeping the outbreak going," he added.

"The next few days will be critical. All of us must do our part, in order to defeat Covid-19."

In his post, Mr Lee also addressed the issue of migrant worker dormitories, where the vast majority of new cases were found.

As measures to break the chain of transmission there will take some time to show results, Singaporeans must expect to see more cases from dormitories for a while longer, he said.

"But we are building up our healthcare and isolation facilities to handle the load," Mr Lee said.

He added that the migrant workers who are ill are getting the medical treatment they need. "Fortunately, the vast majority of the cases are mild, because the workers are young. Our healthcare teams continue to monitor their conditions."

On Friday, the Health Ministry (MOH) announced 623 new coronavirus cases in Singapore, bringing the total to 5,050. Foreign workers staying in dormitories made up 558 of the 623 new cases, or nine in 10 new patients.

The MOH also said it was concerned that it is increasingly difficult to link the new cases and identify sources of infection.

The number of unlinked cases in the community has increased slightly, from an average of 19 cases per day in the week before, to an average of 22 per day in the past week.

"We have an ongoing surveillance programme, where a small sample of patients at our primary care facilities are tested for Covid-19 infections," said the MOH. "We have picked up some cases through these tests, which is an indication of undetected cases in the community."