A worksite in Seletar Aerospace Heights is now connected to four cases after two more people who had been to the site were confirmed yesterday to have the coronavirus.
All four cases are Bangladeshi.
The two new cases are aged 30 and 37, and both have no recent travel history to China.
The 37-year-old, who worked at the site and was identified as a close contact to the two previous cases, fell ill on Feb 7 and was taken by ambulance to Tan Tock Seng Hospital on Feb 11.
The man reported that he had mostly stayed in his rental apartment in Campbell Lane since he fell sick.
Contact tracing is ongoing for the other case, though he is linked to the same worksite.
The works at the site are to extend Bombardier Aviation's service centre at 7 and 8 Seletar Aerospace Heights, said a spokesman for the manufacturer.
A spokesman for Boustead Projects, which is overseeing the project at the site, said earlier that the first two cases linked to the site are employees of a sub-contractor.
Three of Boustead Projects' employees are currently under quarantine, and the project site is operating with additional health measures such as temperature screenings, he added.
All mass meetings at the company's worksites have been suspended, and measures such as preparing back-up staff to take over duties from those under quarantine or on leave of absence have been taken since Singapore's disease outbreak response level was raised to "orange" last Friday, the spokes-man said.
The first Bangladeshi worker, 39, who stayed at The Leo Dormitory in Kaki Bukit, tested positive for the virus on Feb 8.
The second worker, a 39-year-old man, first reported symptoms on Feb 6, and had stayed at his rental apartment in Veerasamy Road before being admitted to the National Centre for Infectious Diseases on Monday.