But 12-car trains will continue to run southbound during morning peak hours, with the date of full transition depending on how well passengers adapt, MTRC's head of operations Sammy Wong Kwan-wai said yesterday.

The transition to shorter trains and a new signaling system on February 6 was to prepare for the East Rail Line's extension across the harbor to Admiralty as part of the Shatin to Central Rail Link.

He said so far the East Rail's capacity is enough to cope with passenger demand.

"At Tai Wai station, an interchange station between Ma On Shan Line and East Rail Line, a majority of passengers are able to board the train immediately," Wong said.

However, he admitted that the rail operator will stick to using longer trains during the morning rush hour.

"We have made special arrangements, such as special services from Sha Tin and Tai Wai during rush hour between 8am and 9am," Wong said.

"After commuters adapt to the arrangements with nine-car trains, we will start to deploy more and more nine-car trains during rush hour and eventually fully switch to them on the East Rail Line."

Yesterday, a commuter who was changing from the Tuen Ma Line to the East Rail Line said he was not able to board the nine-car train at Tai Wai station.

"The 12-car trains are better, as the nine-car trains are more crowded and always full I have to leave home a bit earlier now since the switch," he said.

The new signaling system also saw hiccups after it was put into use, as it mistakenly set off alarms on trains, running red lights on multiple occasions.

Wong said there may be problems and delays initially but the team has been working hard to improve the system with the contractor and hopes that the cross-harbor section can be opened as soon as possible.