Rosarin Plianlar was killed when she dropped onto the track shortly before 7am.

“My wife had severe morning sickness. Often, she felt dizzy and felt faint,” her husband Piyapong Rorbkorb was quoted by police as saying.

CCTV footage at the station showed Rosarin was in front of a row of waiting passengers when a train was about to arrive. She was initially behind the yellow line at the platform, but then it looked like she moved a few steps forward and dropped into the track.

It was unclear whether she had fainted and fallen onto the track.

SRT Electrified Train president Wisut Chanmanee said the train was only about 50 metres away when Rosarin fell onto the tracks.

The driver pressed the emergency brake button, but did not have enough distance to stop the train in time.

The system requires about 100m for a train to be brought to a halt in an emergency, he said.

SRT Electrified Train has planned to install platform screen doors at all stations of the Airport Rail Link.

At present, however, these doors are available only at Suvarnabhumi Airport station.