A 68-year-old Singaporean man, who was announced yesterday as a new imported coronavirus case, is being investigated for not declaring he had symptoms.

The Ministry of Health (MOH) said in a statement yesterday that investigations are being done to assess if there has been any breach of travel requirements.

The man had travelled from Indonesia and had been having shortness of breath since Nov 11.

But on Tuesday, he said in his health declaration form for immigration clearance that he did not have any symptoms.

"We urge everyone to continue to exercise social responsibility and will not hesitate to take enforcement actions against those who breach the rules," said MOH.

The Singaporean man is one of four new coronavirus cases announced yesterday, all of whom were imported. There were no new locally transmitted cases for the ninth day in a row, the longest such period since a 12-day streak from Jan 23 to Feb 3.

Yesterday's figure takes Singapore's total to 58,139.

The new imported cases were placed on stay-home notice on arrival in Singapore.

They include a special pass holder, a permanent resident (PR) and a work permit holder.

The special pass holder arrived from Montenegro to board a ship docked here as a crew member. The PR came from India, while the work permit holder arrived from Indonesia.

Other than the Singaporean, all the imported cases were asymptomatic when tested.

MOH also said yesterday that of the 28 Covid-19 patients in hospital, one is in critical condition in the intensive care unit. This is the first critical case in just over a month since Oct 11.

Together with the 31 patients recuperating in community facilities, Singapore has 59 active cases.