SINGAPORE - Thick smoke was seen at the Tanjong Pagar MRT station on Monday (Aug 15) afternoon, affecting one trainload of passengers.

A leak of freon gas from the train's air-conditioning system caused the smoke, SMRT said in a statement. No injuries were reported, said the Singapore Civil Defence Force (SCDF).

"At 2.53pm this afternoon, passengers at Tanjong Pagar MRT station were detrained from a westbound train due to a leak of freon gas from the train's air-conditioning system," said Ms Margaret Teo, SMRT's head of corporate marketing and communications.

"SMRT staff switched on the tunnel ventilation system immediately to disperse the odourless gas."

Freon, a common refrigerant, is odourless and has low toxicity. It does not catch fire.

The train was withdrawn from service and its air-conditioning system is being checked, said SMRT. It was towed to Ulu Pandan Depot, according to police.

There was no service disruption as the passenger platform at Tanjong Pagar MRT station "remained in service during this incident", said SMRT.

"We apologise to passengers affected and will be investigating the cause of this incident," said Ms Teo.

Passenger Sophia Kee said the train compartment she was in became smoky during the journey between Raffles Place and Tanjong Pagar stations.

It appeared to be "coming from underneath the train", from the gap between the train and the tracks, she told The Straits Times.

The smoke filled the train and the station as far as she could observe.

"It was really strong, thick smoke," she said, adding that it set her coughing.

Ms Kee, 30, an environmental designer, said she and the other passengers did not know what to do when the train stopped and the train doors opened.

"We did not know if it was more dangerous on the train or off the train," she said, adding that there were no announcements telling passengers what to do while she was there.

After about one minute, she decided to get off the train and walk to her office in Outram Park. As she left, she saw SMRT staff arriving to help the passengers.

There was no fire detected and its assistance was not required for the incident, SCDF said.

"Arising from a video footage sent by a commuter showing a smoke filled station platform at Tanjong Pagar MRT Station, SCDF immediately contacted SMRT which confirmed that the smoke has since dissipated and SCDF's assistance was not required," it said in a statement on Facebook.

"As a precautionary measure, SCDF deployed its resources to the train station to investigate on the matter. There is no fire detected and no sign of smoke now at the station. Train service to the station is also not affected."

Police said it is looking into the incident.