Earlier, interest-free loans were announced for Emiratis whose businesses were affected by the rains, with a grace period of 6 to 12 months
The country has won praise for its handling of the outbreak, and had largely kept the crisis in check by carrying out large numbers of tests and tracing close contacts of those infected.
Authorities had slowly been introducing curbs, such as closing nightclubs, but had so far avoided the kind of tough restrictions seen in worse-hit nations.
However, after a jump in the number of locally transmitted cases in recent days, Prime Minister Lee Hsien Loong said it was time to apply a "circuit breaker" to halt the virus's spread.
Workplaces except for essential services, such as supermarkets and hospitals, and those deemed to be in key economic sectors will be closed from Tuesday, he said in a televised address.
Schools will also be closed from next week except for children of those who have to continue to work and cannot make alternative arrangements, he said.
People are being told to stay at home as much as possible, and only go out for essentials - such as buying food and getting exercise.
"Looking at the trend, I am worried that unless we take further steps, things will gradually get worse, or another big cluster may push things over the edge," Lee said.
Singapore has reported 1,114 virus infections including five deaths. Globally, the number of confirmed cases has soared past one million and deaths have topped 50,000.
Earlier, interest-free loans were announced for Emiratis whose businesses were affected by the rains, with a grace period of 6 to 12 months
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