A station platform screen door on the eight-month-old Downtown Line 2 was dislodged from its frame yesterday, causing a two-hour stoppage in services during the morning rush.
It was the fourth major rail incident in five weeks.
Operator SBS Transit said service was disrupted at 6.25am, and did not resume until 8.25am, when the unhinged and shattered glass door at the Sixth Avenue station was removed. The affected section was cordoned off, and safety tape put across the gap where the door used to be.
During that time, trains could not pass through the Sixth Avenue station towards Chinatown.
An SBS Transit spokesman said it does not know how the door - supplied by Faiveley Transport of France - was dislodged, but said it will be "investigating the cause" with the Land Transport Authority (LTA) and the contractor.
An LTA spokesman said: "This is the first time an incident of this nature has happened."
Work at the Sixth Avenue station was disrupted when contractor Alpine Bau of Austria went bust in mid-2013. The insolvency was supposed to have delayed the opening of Downtown Line 2 by six months to the middle of this year, but engineers put in extra shifts to get the line opened on Dec 27.
Yesterday, SBS Transit tried to mitigate the impact of the service disruption by running free bus bridging services between King Albert Park and Sixth Avenue stations - where trains could not pass.
The incident was the second within six days to hit Bukit Panjang residents, who faced a day-long glitch on the Bukit Panjang LRT last week.
The breakdown happened on the day of the Primary School Leaving Examination science paper, as well as several exams for N-level students. According to the Singapore Examinations and Assessment Board, "fewer than 10" pupils taking their N-level exams were late because of the disruption.
Public relations executive Ashley Wu, 35, said that when commuters saw a sign SBS Transit put up at Bukit Panjang station saying there would be no train service from King Albert Park to Chinatown stations, many switched to taxis or buses.
Ms Wu said she took bus service 75 to Holland Village and switched to the Circle Line to get to work in Haw Par Villa. "I was an hour late."
She said she did not go into the station to get a breakdown chit "because it was quite chaotic".
