Metro operator SMRT said police were called in Monday after a man wielding a samurai sword jumped a fare gate at a suburban station and boarded a train headed towards the city.

A police spokeswoman said he was detained for possession of a weapon, an offence which is punishable by up to five years in jail and a mandatory minimum of six strokes of a cane.

She did not respond to queries about his nationality or age.

Photographs posted on social media by other passengers on the train showed the man wielding the sword while dressed in a white T-shirt and Japanese "hakama" pants usually worn by martial arts practitioners.

He appeared to sport frizzy, shoulder-length hair. "From the waist up he looked like a rocker, but from the waist down, he looked like a samurai," witness Kim Bomhae told the Straits Times newspaper.

The images posted on Facebook and various blogs showed police officers and passengers keeping a wide berth as the man brandished the unsheathed sword on board the train.

He was apprehended by police who tailed him after he alighted at City Hall station at the heart of Singapore's civic district.

The bizarre incident immediately drew online derision. "Seems like a good way to ensure you get your personal space on the train," wrote Ahmad Zhaki Abdullah on the Straits Times' Facebook page.

Congestion on the 150 kilometre-long (93-mile) metro network has fed resentment among Singaporeans in recent years.