SINGAPORE (Reuters) - Singapore made it mandatory to wear masks in public from Tuesday to prevent the further spread of the new coronavirus, a turnaround from authorities’ initial advice as evidence grows that undetected cases may be more prevalent than thought.

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When the virus broke out in the city-state nearly three months ago, officials told locals to wear masks only if they were sick, to avoid transmitting the infection. But in the last few days, authorities have started advising the use of masks and made them compulsory in certain places like public transport.

“The minute you leave your house, you have to wear a mask when you go out,” Lawrence Wong, a minister who co-heads Singapore’s virus fighting task-force, said on Tuesday.

He cited potential undetected cases and the risk of the virus being spread by people who do not show any symptoms.

First-time offenders caught without a mask will be fined S$300 ($212).

Exceptions will be made for children with special needs or aged under two as well as for individuals engaging in strenuous exercise outdoors.

The government has distributed reusable masks to households, while conserving surgical masks for healthcare workers.

Authorities confirmed 334 more coronavirus cases on Tuesday, mostly linked to outbreaks in migrant workers’ dormitories, taking its tally to 3,252.

Singapore is in a partial lockdown to control the spread of the coronavirus, with schools and most workplaces closed for a month from last week to try to control the spread of the virus.

Essential services and some businesses are still allowed to operate although the government is looking to tighten further the list of companies permitted to work in order to minimise the movement of people.