Bars, cinemas and all other entertainment outlets will be closed from 11.59pm tomorrow until April 30 at least, as Singapore's fight against Covid-19 enters a new phase amid a wave of imported cases.

The multi-ministry task force set up to combat the outbreak announced sweeping changes to limit gatherings, protect the vulnerable and strongly discourage travel.

So, tuition and enrichment classes at centres as well as all religious services will be suspended.

People will have to limit gatherings outside of work and school to 10 persons or fewer, while malls, museums and restaurants must reduce crowd density to stay open.

In addition, with about 1,000 residents and long-term pass holders here still travelling abroad daily despite advice not to do so, those who leave the country from Friday will have to pay unsubsidised rates should they be hospitalised for Covid-19 treatment.

Singaporeans must take the measures very seriously, said task force co-chairman and National Development Minister Lawrence Wong. The measures are pre-emptive, but come at a time of real risks, he stressed.

"All over the world, millions of people are living in a different reality. Workplaces are closed, shops are empty, roads are empty, everyone is asked to stay home," he said.

Singapore had not reached this point, but the risk of local transmission will rise with more imported cases, he said. "So, we have to take seriously the measures to protect our family members and the people around us."

He called for everyone to stay at home as much as possible.

"Stay at home as much as you can, and go out if you need to work, go to school, go out for essential tasks - but otherwise stay at home, reduce your social gatherings and all other activities for the next one month," he said.

The measures come as 49 new Covid-19 cases were reported yesterday, including 32 imported cases, bringing the total of people found to have the virus here to 558.

From 11.59pm today, all Singapore residents returning from Britain and the United States - two at-risk places from where people are flooding back, will have to stay in hotels to serve their 14-day stay-home notice.

Those who breach the rules face fines of up to $10,000 or jail for up to six months, or both.

Health Minister and task force co-chairman Gan Kim Yong stressed that cases all over the world are still rising and have not peaked yet, so the number of cases here may grow.

"We really want Singaporeans to understand that we are serious about implementing and enforcing these measures. We encourage them to work with us, and we hope we do not have to resort to enforcement actions."

However, if required, the sweeping measures may be escalated to include suspension of schools and workplaces.

Mr Wong warned: "Closure of schools, closure of workplaces, other than essential activities - that is the most drastic step. That is what I suppose people call a 'lockdown'. And that set of drastic measures may well be necessary."

Noting that schools have already stopped co-curricular and enrichment activities, the Health Ministry's director of medical services Kenneth Mak noted that these are calibrated moves.

"But as the risk changes over time, and if we assess that the risk to students changes, then there may be a need for adjustment of that particular posture."

Tomorrow, Deputy Prime Minister Heng Swee Keat will present a further set of measures aimed at preserving jobs and livelihoods, helping viable companies stay afloat and supporting households amid the battering Singapore and the world are facing. More support will be given to the most severely impacted sectors, he said in a Facebook post last night.