Lawmaker Gary Zhang on Tuesday said emergency exits on MTR trains should only be used in emergencies, for example if the train's on fire or a terrorist attack is taking place.

His warning comes after 20 people left an Island Line train via an emergency ramp on Monday evening when the normal doors failed to open at Wan Chai Station.

"They [emergency exits] are designed for extreme situations. They are definitely not designed for a normal technical equipment fault," Zhang said, adding that using an emergency exit is very dangerous.

Monday's incident led to services being suspended between Sheung Wan and Quarry Bay for almost an hour.

Zhang, who used to be an engineer with the railway company, told an RTHK programme that drivers need permission from the control centre to manually open train doors, and this can take some time.

"Normally when a train arrives at a station the doors open immediately. So to passengers, even if the waiting time is only like two or three minutes, they might feel longer than it actually was. According to our knowledge, the emergency exit ramp was actually operated after the train arrived at the platform, just two minutes later," he said.

When asked whether a lack of information may have caused passengers to panic, Zhang said MTR bosses may need to review the Standard Operating Procedure (SOP).

"According to the current SOP, when a technical issue happens, the train captain will first get in touch with the control centre and seek authorisation for manual handling. And then before the train captain does the manual handling, he will need to make a passenger announcement to remind the passengers that the train movement will happen", he told RTHK.

"But in yesterday's incident, when the train captain was still communicating with the control centre, the emergency exit door was already operating. That might be worth some sort of review of whether the SOP should be updated so that the train captain can make announcements to make the passengers calm first and then make communication with the control centre to seek authorisation."

Zhang added that future generations of trains equipped with a function that enables direct communication between the control centre and passengers could help in similar situations.