Coronavirus cases in Singapore topped 30,000 on Friday as the city-state reports hundreds of new infections in cramped migrant worker dormitories every day.

The lowly paid workers represented the vast majority of the 612 new cases reported on Friday, a daily infection rate that is one of the highest in Asia, taking Singapore's total cases to 30,426. The death toll remains 22.

Singapore closed schools and most workplaces in April as part of measures to curb infections. This week, the government published plans for some businesses to resume at the beginning of June, given the low rate of infections outside the worker dormitories.

Businesses with less transmission risk like manufacturing and finance will be allowed to reopen, along with schools. Retail shops and restaurants will remain closed.

The rapid spread of the disease among the migrant labor population appeared to catch Singapore health officials by surprise.

It took the country about three months from the end of January to report its first 10,000 cases, according to a Reuters tally based on official data. The next 20,000 cases were reported in just one month, as testing was boosted in the worker dormitories.

There are more than 300,000 workers from other Asian countries, including Bangladesh, India and China, living in tightly packed accommodation in Singapore.

The daily rate of new infections has slowed to about 600 over the past week, down from a high of 1,426 cases on April 20.

Coronavirus cases and deaths are still well below the Ministry of Health's estimates that about 20% of the 5.7 million population is infected with seasonal flu each year, with an annual average of 600 deaths.