It never snows in Singapore but some MRT commuters are feeling the chill - thanks to ice showers coming from the air-conditioner vents of some trains.

The phenomenon happened on China-made trains plying the Circle Line. The Straits Times understands that there were at least two incidents last month.

On a train heading from Bartley to Kent Ridge on a Saturday morning, ice shards - some the size of a little finger - blasted from a vent. The train was evacuated mid-journey.

The second incident took place on a Monday afternoon on a train from Bras Basah to Serangoon, when ice particles fell from above.

The trains were designed by French manufacturer Alstom and assembled in China. Their air-conditioning system was jointly designed by Alstom and Chinese equipment supplier King.

The Land Transport Authority told The Straits Times it was aware of the freezing flaw, and was taking steps to rectify it.

"The forming of the ice particles was caused by the excessive cooling of the air-conditioning system," said an LTA spokesman. "Rectification works are being carried out, and we are also conducting fleetwide checks as a precautionary measure."

She added that there was no impact on train operations as the rectification works and checks are done concurrently when the trains are undergoing their scheduled preventive maintenance.

She also said such problems are not specific to trains, and "can happen to home air-conditioning systems and refrigerators".

Professor Choo Fook Hoong of the Energy Research Institute at Nanyang Technological University said that while the phenomenon does arise, "it is not common".

"Usually, it's when the sensor is faulty and it is not detecting temperatures accurately," he said, adding that the air-con would then run continuously and humidity in the air condenses before ice forms.

Prof Choo said the flaw is relatively easy to fix - by replacing the faulty sensor.

Rival transport group ComfortDelGro Corp said it has encountered ice forming on the air-con vents of its Downtown Line trains too.

Last month, there were also reports of water streaming down from the air-con vents of an East-West Line train.