Trains should be less crowded from this week, after the Land Transport Authority (LTA) "fine-tuned" service frequency on Monday following an outcry from commuters last week.

The LTA said trains will now run every three minutes during peak hours, down from five minutes last Friday - the first day of adjustments made to reflect lower demand following heightened safe distancing measures.

The five-minute frequency caused crowding on lines such as the North-South, East-West and Circle lines, triggering complaints by commuters who posted pictures of packed trains on Facebook.

This prompted Transport Minister Khaw Boon Wan to step in. Mr Khaw said on Saturday: "I have told LTA to err on the side of generosity. That is, to over-provide rather than under-provide."

Before the pandemic, trains ran at intervals of two minutes or less during peak hours.

"Ensuring that commuters can maintain a safe distance from one another when on board our trains and buses during the circuit breaker period remains a priority," an LTA spokesman said. "LTA and the public transport operators will continue to monitor the situation and fine-tune rail service capacity as necessary."

At the Serangoon interchange between 8.25am and 9.45am yesterday, there was significantly more commuter traffic on the Circle Line (CCL) platform than on the North East Line (NEL) platform.

Trains were observed arriving within two minutes on the NEL, and between three and four minutes on the CCL. On NEL trains, commuters were able to practise safe distancing with relative ease, while on CCL trains, this was not always the case.

Meanwhile, the LTA said public transport commuters should continue wearing masks even after the heightened safe distancing measures are lifted.

It said that when crowds return after the circuit breaker period, safe distancing would not be "easily achievable". As such, "a practical compromise is for all commuters to continue wearing masks on public transport".

The authority has not made further adjustments to train frequency during off-peak hours, which remains at around 10 minutes, nor to bus services.

A Ms Ling Lng posted on Facebook a photo of a packed Service 89 on Monday, complaining that with Service 89e removed, Service 89's frequency should have been increased. "Though fewer people are commuting to work, you can't reduce the bus capacity to half and expect passengers to abide by social distancing," she wrote.