MTR services along the Tsuen Wan Line ground to a halt after platform screen doors at Yau Ma Tei station jammed, emitting sparks and smoke.
One woman arriving much later at the station was sent to hospital. Many passengers found themselves locked in the carriages during the morning rush, at about 8.10am.
As MTR staff rushed in to cope with the problem passengers were instructed to use the other doors on the platform.
But an hour later, other doors on the same platform also broke down, failing to open and close properly. Rail staff manually opened all the doors. Trains had to slow down, delaying services by 10 to 15 minutes.
The delays made it more crowded than usual in carriages as well as on the platform.
At around 9.40am, a woman fell sick after traveling from Mei Foo to Yau Ma Tei.
She was sent to hospital upon arrival in Yau Ma Tei.
The problem was fixed at around 10.20am and normal services on the Tsuen Wan Line slowly resumed.
A spokesman said engineers would continue to monitor door operations. A thorough inspection and maintenance were to be carried out overnight.
A passenger, Mayce Cheung, said the train kept stopping all along the way but announcements did not say what was wrong.
"I was late for my appointment so I decided to get off at Mong Kok and walked to Yau Ma Tei instead," she said.
"It was so hot and crowded inside the train."
Another passenger said the train was moving very slowly, taking 40 minutes to travel from Mei Foo to Yau Ma Tei, which usually takes 13 minutes, according to the MTR mobile app.
Another commuter said the platform at Mong Kok was so crowded she had to wait more than 15 minutes for a train to Central. "So many delays and breakdowns recently but all they [MTR Corp Ltd] do is to increase the fare," she complained.