Passengers caught up in a drama on the MTR on Sunday morning should not have used an emergency exit to escape into the tunnel, according to lawmaker and former engineer at the railway company, Gary Zhang.

Some 750 passengers were on board a Tsuen Wan Line train when two sets of doors were ripped off a carriage at Yau Ma Tei Station.

While the vast majority of the passengers managed to leave the train via the station, about 150 exited through an emergency door at the back of the train and then walked along the tunnel to the next station.

A man surnamed Kwok told RTHK that it was the train driver who told passengers to leave this way.

"The train captain kept telling passengers to calm down and said there was smoke. We didn’t know what happened. After a while, he told us to disembark from the rear of the train and walk back to Mong Kok along the track," Kwok said.

"After we opened the doors, we didn’t know whether we should wait for staff members to come show us the way, or whether we should start walking. We were very confused. The public announcement was unclear. We waited but no one showed up so we left the train. We didn’t know what they wanted us to do."

Kwok added that the tunnel was very dark and passengers used the torches on their mobile phones to see where they were going.

One woman, 78, suffered abrasions while in the tunnel and was taken to hospital, and another felt unwell.

However, Zhang told RTHK that there was no need for any of the passengers to go into the tunnel.

"This is not favourable at all, because we know the tunnel environment is not really for people to stay. There are a lot of hazards and unexpected risks. Only in very, very extreme situations, like fire or heavy smoke, is this the last resort as the way out," he said.

"In today’s case, it is very clear that there was no imminent risk in staying in the train. A more favourable option was to evacuate the passengers using the platform."

Zhang said the government and MTR should better educate the public about when it is appropriate to use emergency exits on trains.