The Downtown Line was hit by a signalling fault early yesterday morning.

The glitch caused a service delay across the entire MRT line from as early as 7.45am, with commuters down the line from Bukit Panjang all the way to Bedok complaining.

Train service started to return to normal just past 9am, over an hour after the glitch. Photos of packed station platforms were circulated on social media.

SBS Transit first sent out a public alert at 8.30am. "Downtown Line is delayed due to a signalling fault. Please expect additional 10 mins of travelling time. Free bus rides at designated bus stops are available. We are sorry," it said.

About 15 minutes later, SBS Transit tweeted that commuters travelling from Bugis to Little India, towards Bukit Panjang, should add at least 20 minutes to their journeys.

At 9am, SBS Transit said service on the Downtown Line was back to normal. Later at 9.20am, it said that free bus services had ended and apologised for the incident.