'A train was approaching the station when it happened, and the train driver also saw the passenger and so he stopped the train,' the spokesman said.

'After the train stopped, our platform staff then went down to the track and led the passenger back to the platform, from where he was taken to hospital by ambulance.'

The trespasser was not injured, but was admitted to United Christian Hospital for a check-up. He was later discharged.

A witness, Chan Hei-ting, a student at Shue Yan University, said many passengers on the train were worried about the man's safety.

Police were able to contact Wong's family through information sewn on his pullover.

His father, Wong King-hung, said his son came to Hong Kong two years ago from Zhaoqing and the family of four now lived in a cubicle in Ngau Tau Kok.

He said his son became mentally disabled after having a fever when he was seven.

'I really hope a school in Hong Kong can take my son. No sheltered workshop or a school wanted to admit him,' he said. 'It is very difficult to keep an eye on him all the time.'

Wong said his son had a record of going missing from time to time, and had once gone missing for three months.

'He sometimes climbs water pipes installed on the outer walls of buildings at Lok Wah Estate,' Wong said.

'I always have to find him when he has gone missing ... wondering if he is alive or dead.'

After this comment from his father and when the media were still interviewing him at their home, Ho-keung disappeared.

He said he was going to the bathroom - and left the home.

He was not found until about 5pm, when he was seen climbing on a water pipe near the seventh floor of a building on Lok Wah Estate, where his grandmother lives.