A 39-year-old man who refused to wear a mask while on the MRT train was arrested by the police on Sunday for allegedly causing public nuisance and flouting safe distancing measures.
In a video circulating on social media, the man is shown telling fellow commuters loudly: "I'm very religious... I hate seeing uncles, granddads with a mask on."
When a fellow commuter offers him a mask, the man rejects it.
The video also shows a commuter leaving her seat when he takes the one next to her.
Education company director Jerome Tan, 61, who took the video, said the incident happened last Friday around 11.15pm. He was on a train heading towards Joo Koon when the man got on.
"He was talking to an old man, trying to convince him to take off his mask, saying it'll make him sick," said Mr Tan.
The man was still on the train when Mr Tan alighted at Redhill MRT station around 11.20pm.
He said he approached the MRT station master and told him about the unmasked commuter.
The station master told him he would call the next station to inform the staff of the incident.
Mr Tan said the man's refusal to wear a mask put others at risk: "What's worse is that he tried to convince others not to wear masks, and I found his attitude quite arrogant - something had to be done."
The police said investigations are ongoing. "Everyone should take the safe distancing measures seriously. The police will not tolerate such blatant disregard of the law and wilful breaches of safe distancing measures," they added.
Rail operator SMRT said in a Facebook post on Sunday that it had made a police report about the incident. It added that staff who are alerted to such incidents would ask commuters to wear a mask properly.
If commuters do not comply, the Public Transport Security Command would be activated, SMRT said.
"We do not condone socially irresponsible behaviour that affects the safety of others, and strongly encourage our commuters to keep their mask on at all times and avoid talking on trains."
First-time offenders who breach laws under the Covid-19 (Temporary Measures) Act can be jailed for up to six months and fined up to $10,000.