Commuters try and get up on buses at the bus stop below Queenstown MRT after train service stopped.

The Land Transport Authority (LTA) has ordered rail operator SMRT to check all its service maintenance doors after one came loose and disrupted train services on the North-South and East-West Lines (NSEWL) from about 6am until noon yesterday.

At 11.30am, train services between Queenstown and Bugis MRT stations on the East-West Line were halted for 30 minutes as traction power had to be switched off to enable engineers to access the tracks safely to fix the problem.

Normal train service resumed progressively after the door was removed at noon.

Yesterday's incident was the ninth reported delay affecting the train system this month, leaving transport experts concerned about the recent spate of faults.

Rail operator SMRT said in a statement on Facebook at 11.15am that the affected MRT lines had experienced intermittent traction power tripping across the network.

The fault was traced to a loosened service maintenance door next to the tracks in the tunnel near Tiong Bahru station, said the LTA in a statement.

The Straits Times understands the intermittent power trips were caused by a sliding door separating the east and westbound tunnels that had become dislodged from its roller rail.

"We decided to remove the door as it was faster than repairing it. This allowed train services to resume as quickly as possible," an LTA spokesman told ST.

LTA is investigating the incident, which was not related to ongoing tests of the new signalling system on the NSL that began on May 29.

Free regular bus services were made available between the two affected stations.

The delays left commuters fuming and late for work.

Ms Jasmine Lew said on SMRT's Facebook page that she was stuck in a train at Simei station, and "waited in the poorly lit train that also had no air-flow for almost 45 minutes".

Ms Florence Yun, 25, a valuation analyst, told The New Paper that she took 40 minutes to get from Jurong East to Buona Vista station, where she got off.

"It's been happening frequently so honestly it's not a surprise any more. SMRT needs to get their act together," she said.