Singapore confirmed 23 new cases of COVID-19 on Sunday, of which 18 are imported and five are local cases.
This brings the national total to 455 cases, said the Ministry of Health (MOH) in its daily update.
The imported cases had travel histories to Europe, North America, South America and ASEAN (Association of Southeast Asian Nations) countries. All except one case were returning residents and long-term pass holders.
Four more patients have also been discharged, the MOH said.
In all, 144 people have fully recovered from the infection and have been discharged from hospital. Of the 309 confirmed cases who are still in hospital, most are stable or improving. Fourteen are in critical condition in the intensive care unit.
The first two deaths were reported Saturday morning.
On Sunday, the city state also announced tighter border controls, in a bid to reduce further imported COVID-19 cases.
Singapore will bar all entry and transit to all short-term visitors starting from 11:59 p.m. Monday, the MOH said in a statement.
Previously, except for a handful of countries, short-term visitors from elsewhere were allowed to come into Singapore, although they would be given a 14-day Stay-Home Notice (SHN) upon arrival.
In light of the heightened risk of imported COVID-19 cases into Singapore, the ministry said this move will help to "conserve resources so we can focus on Singaporeans."
The MOH also noted the "further sharp increase" in cases globally and widening spread. To date, there are more than 260,000 COVID-19 cases across 185 countries and regions, and around 11,200 deaths.
In Singapore, almost 80 percent of cases in the past three days were local residents or long-term pass holders returning from overseas. These imported cases had travel histories to 22 different countries.
In addition, only work pass holders providing essential services, such as in healthcare and transport, will be allowed by the Manpower Ministry to enter or return to Singapore. This will include their dependents.