Taipei, Aug. 6 (CNA) Passengers using Taipei's mass rapid transit (MRT) system are required to wear masks for the duration of their trip with immediate effect, regardless of whether they can maintain social distancing, Taipei Rapid Transit Corporation (Taipei Metro) said Thursday.

Anyone who fails to comply to the reinstatement of the compulsory mask wearing rule, which came after several foreign nationals tested positive for COVID-19 after returning to their home countries from Taiwan, will be denied service and potentially fined up to NT$15,000 (US$511), Taipei Metro said.

Three foreign nationals, two from Japan and one from Thailand, were diagnosed with COVID-19 after returning home from Taiwan in June, July and August.

Two of those cases, involving a Japanese student and a Thai worker, were closed Wednesday, with the Central Epidemic Command Center (CECC) concluding that they posed no risk of community spread in Taiwan.

However, the case of a Japanese engineer, who tested positive for COVID-19 after returning to Japan on Aug. 1, is still being investigated, as is the case of a Belgian man who tested positive last week in Taiwan, according to the CECC.

The CECC reiterated that people should wear masks in enclosed spaces, including medical care centers, public transportation, schools, religious centers, markets, performance centers, entertainment centers, and areas where large numbers of people gather.

Compulsory mask wearing on the Taipei metro was relaxed on June 7, at a time when no new domestically transmitted coronavirus cases had been reported in Taiwan since April 12, according to CECC data.

During that period, passengers did not have to wear masks on the metro system if they could maintain social distancing of at least 1.5 meters between themselves and other passengers.

However, wearing masks for the duration of the trip remained obligatory for passengers who had a fever or cold symptoms.