Four wheels of an MTR East Rail train derailed as the train returned empty to a depot on Thursday night.
The wheels of a bogie on the train's eighth car came off the rails as the train was negotiating a sharp bend at the southern entrance to the Ho Tung Lau depot in Fo Tan at 11.20pm.
The railway operator said it informed the Electrical and Mechanical Services Department immediately and sent engineers to put the wheels back onto the track.
A spokesman said the SP1900 train, the bogie and the track were inspected and found normal. It might have been caused by the sharp curve and a lack of lubricant, he said, adding that there were no such curves on tracks where passengers were carried. The incident, which came a week after a broken power cable at Yau Ma Tei station disrupted services for three hours, brought a call from a lawmaker for the MTR not to downplay incidents in its depots.
The spokesman said the rail operator was now conducting checks on all SP1900 trains and rail lubrication in the depot. The train had undergone major maintenance in June and bogies were checked every 23 days.
He said it was a rare incident and had not occurred since the merger of the MTR and the Kowloon-Canton Railway - the former operator of East Rail - in 2007.
Lo Kok-keung, an engineer from Polytechnic University's mechanical engineering department, said that when a train made a turn, a side thrust was exerted on the flange of a wheel and if the flange was insufficiently lubricated the friction might cause the wheel to slip sideways. Lawmaker Andrew Cheng Kar-foo criticised the government and the operator for overlooking MTR breakdowns.
'I believe it is not the first time for this kind of incident to happen inside a depot. I remember once two trains crashed in a depot,' he said. 'Although there were no passengers, the driver was there and we have to be concerned about his safety. It just cannot overlook incidents on the tracks in depots because there were no passengers.'
Cheng suggested a mark-deduction system to penalise the operator if too many faults occurred. The power breakdownlast week also cased traffic chaos as the MTR laid on shuttle buses for stranded passengers.