Hong Kong’s rail operator is under pressure to explain whether human error was behind a 1½-hour partial shutdown of the Island line on Wednesday and to strengthen staff training to prevent similar incidents in the future.

Ex-lawmaker Gary Zhang Xinyu, a former MTR Corporation engineer, said on Thursday that the previous day’s disruption was very likely to have been caused by non-compliance with maintenance protocols.

“The coming investigation should focus on whether maintenance protocols were strictly followed,” Zhang, now director of the Smart Transportation Alliance, told a radio show.

“Unless they encountered an unprecedented mechanical failure, the chances of human error are nowhere near low.”

Train services between Sheung Wan and Quarry Bay stations were suspended shortly after the Island line began operating at 6.07am on Wednesday. They resumed at 7.30am.

The MTR Corp said items from a maintenance vehicle and damage to track equipment caused the disruption, describing the incident as “rare”.