Serious corrosion at the mounting bolts and nuts of a metal barrier caused it to dislodge, leading to a partial train derailment last year, according to a detailed investigation report released by the MTR on Thursday evening.

Several doors were ripped off a carriage as the train pulled into Yau Ma Tei station in November, disrupting train services on the Tsuen Wan Line that day.

Around 150 passengers left the train via an emergency exit and walked along the tracks to Mong Kok Station through the tunnel.

According to detailed findings, the metal barrier that the train hit was displaced due to seriously corroded mounting bolts and nuts at the structure's base frames on the ground and the tunnel wall.

"There is no registration of the incident barrier and those of similar design intent in the asset management system due to inadequate granularity in categorising the civil structure assets for addressing them specifically,” the report by the investigation panel said.

“Hence there is no specific maintenance instruction to staff for inspection of such, nor regular asset condition and train operation impact assessment conducted specific to the barrier," it noted.

The probe also found that a public announcement following the accident failed to let passengers know where they should exit the train, as it "did not adequately express the intended message of detrainment to the platform of Yau Ma Tei Station".

In response, the railway company vowed to implement the recommendations by the panel.

"In the wake of the recent incidents, the corporation is conducting the comprehensive reviews on our asset management and maintenance regime, as well as the comprehensive trackside infrastructure and equipment survey, to reassume that we maintain the highest safety standard,” its operations director Tony Lee said.

"We are progressively upgrading or replacing all 57 metallic protection barriers of similar nature and conducting specific maintenance on the barriers."

The MTR also said it is taking action to add a function on all trains to send an alert directly to the control centre when a ramp at the emergency exit is used, adding that it has enhanced training for staff members on how to evacuate passengers effectively.

"The corporation will also enhance the dissemination of passenger information at stations and free shuttle bus routes during incidents," it said.

The government, meanwhile, said it received the detailed report submitted by the MTR.

In a statement, a spokesperson said authorities will follow up on the comprehensive trackside infrastructure and equipment survey by the railway company, which is expected to be completed by mid-May.

"The [Electrical and Mechanical Services Department] will closely follow up with the [MTR Corporation] on the progress of implementing the various recommendations proposed in the report to prevent recurrence of similar incidents," it said, adding that an independent panel is monitoring a comprehensive review conducted by the MTR.