The man - identified as Theerasak Sittidamrong, 22, a student of Ramkhamhaeng University - was taken to Police General Hospital.

Police found Theerasak unconscious on the track, with serious wounds to his head, back and hips, after being hit by the train. 

Doctors said he was in a critical condition and in a coma.

The Skytrain service was suspended for almost an hour along the main Sukhumvit Line where the incident took place, but operations continued normally on the linked Silom Line.

A notebook found near Theerasak contained a message - presumed to be in his handwriting - in which he appeared to say farewell to his parents, brother and friends. "I did many things wrong, and drank so much that I could not control myself," it read.

Ekkasit Sittidamrong, the 31yearold brother of Theerasak, rushed to the hospital on hearing about the incident.

He said he and his brother had argued the night before about Theerasak's behaviour, at their home in Samut Prakan province. His brother then left the residence at about 2am.

"I just warned him to stop drinking and save his money. We didn't have a serious argument. When he left, he told me not to worry about him. He said he just wanted to go out to meet some friends," Ekkasit said.

This appears to be the first time since the Skytrain began operating in late 1999 that someone has been hit and injured by a train. The system had previously had no major accidents.