Thousands of commuters on the Downtown MRT Line had their journeys extended by as much as half an hour after a signalling fault hit the line yesterday.

Delays on Singapore's newest MRT line were caused by a signalling system fault at the Bayfront station at 6.01am, the Land Transport Authority (LTA) and rail operator SBS Transit said in a joint statement.

"As a result, trains approaching Bayfront station in both directions had to be driven manually and at a lower speed," they added. Delays would persist until the end of passenger service hours.

Signalling systems allow trains to run on schedule, as well as keep them a safe distance apart.

The Downtown Line, as well as the Circle and North-East lines, operate on the newer communi-cations-based train control (CBTC) system.

Last year, the North-South Line, which previously ran on the older fixed-block signalling system, experienced several delays while an upgrade to the CBTC system was being tested.

Though yesterday's fault had been isolated to a stretch between the Promenade and Bayfront stations - one stop apart - in the direction of Expo, by 7.30am, train bunching had resulted in additional travelling time of 15 minutes to half an hour from Bukit Panjang.

Free bus services were provided at designated bus stops between the Bugis and Chinatown stations.

The LTA and SBS Transit said their engineers were working with German engineering giant Siemens, which supplied the signalling system.

"Efforts to restore normalcy along the affected stretch will continue through engineering hours," SBS Transit said in a Facebook post.

Delays affected commuters during both the morning and evening peak periods.

Interior designer Nicole Lim said her ride from Rochor to Downtown at about 6.20pm was "slow and jerky". The 30-year-old added: "The train cars didn't align with the station doors, so we had to wait for the driver to (realign the train)."

Though Ms Lim had experienced delays on the line earlier in the day, she took it again in the evening as she had not expected the problem to continue.

"The train was crawling, especially closer to the central area," said Ms Alex Tay, 54.

The tutor's trip from Hillview to Chinatown, which would usually take around 30 minutes, took more than 45 minutes.

The 42km Downtown Line sees an average of about 470,000 trips a day.

It opened in three stages beginning in 2013, with the third stage opening last October.

On Dec 12, a signalling fault near the Tampines station on the Downtown Line affected thousands of commuters during the evening peak hours.

• Additional reporting by Cheryl Tee