While the number of Covid-19 cases in the community has fallen in recent days, the number of unlinked cases has not come down, suggesting that there is a "larger, hidden reservoir" of cases, said Prime Minister Lee Hsien Loong yesterday.

This is one of the reasons why Singapore has decided to extend the circuit breaker period and implement more stringent measures for the next two weeks, he said.

Singapore has seen a spike in cases recently, mainly driven by an outbreak among foreign workers staying in dormitories.

"We want to bring down the community numbers decisively," PM Lee said in his fourth national address on the ongoing crisis. "We also want to make sure that if any leakage occurs from the dorms to the wider community, we can detect and contain it early, and prevent new clusters from forming and bursting out of control."

Speaking at a press conference after PM Lee's address, Health Minister Gan Kim Yong said the number of unlinked cases in the community currently averages about 20 a day. The Ministry of Health has also been picking up Covid-19 cases from its surveillance programmes, which carry out random tests in the community to identify cases that would have otherwise gone undetected.

"This indicates that there is continued seeding in the community, many of them undetected because the illnesses are mild, symptoms are mild, but they are still infectious," Mr Gan said.

"We are now at the midpoint of the circuit breaker measures. It is therefore very critical for all of us to put in extra effort in safe distancing so that we can break the transmission and further reduce the number of cases in the community."

All standalone food and beverage outlets, as well as hairdressing and barber shops, had to shut by 11.59pm yesterday. Temperature screening will be done at all supermarkets and malls from today, and visitors will have to provide their particulars for contact tracing.

PM Lee also called on Singaporeans to stay home as far as possible, urging those who have to go out to do so alone and not as a group or with family. He acknowledged that many people will be disappointed by the extension of circuit breaker measures.

"But I hope you understand that this short-term pain is to stamp out the virus, protect the health and safety of our loved ones, and allow us to revive our economy."