Officials say they believe a partially derailed train bogie was to blame for an incident at Yau Ma Tei Station on Sunday morning that saw two sets of doors ripped off an MTR carriage, as they warned it could take "a rather long time" to clear the blocked Tsuen Wan Line.

Fire Services’ assistant divisional officer Leung Kam-wah said some 750 passengers were evacuated from the train, with 600 of them leaving via the station and the rest exiting via emergency rear doors and walking along the tunnel to Mong Kok.

An elderly woman suffered abrasions during the evacuation and was taken to hospital, while another felt unwell but did not require treatment. No other injuries were reported.

Chief inspector Tsan Nga-lun from the police told a press briefing hours after the incident that a preliminary investigation suggested no foul play was involved.

Sammy Wong, the MTR's chief of operating, said the driver stopped the train after he heard a noise as the first two carriages pulled into the station.

"After a preliminary investigation, we found that the first bogie of the first train carriage fell slightly off the track. Some components next to the rail are damaged and two sets of doors have come off. We need to examine the train, as well as what components on the platform and rail need to be fixed, after removing the carriages," he said.

Wong said staff would have to inspect the train, the track and other devices before they could give an estimate as to when services could return to normal.

No trains have been running in either direction between Lai King and Jordan since the incident at around 9.30am on Sunday, with reduced frequencies on other sections of the Tsuen Wan Line.

Wong apologised to passengers and promised to find out what went wrong.

“We are very concerned about the incident, and we will conduct an investigation on the incident for more details, and we will update passengers on our investigation findings,” he said.