A localised power trip yesterday morning affected the immigration clearance system at Tuas Checkpoint, causing heavy traffic at the arrival and departure car zones for more than six hours.
The disruption to the system happened at 6.45am, said the Immigration and Checkpoints Authority (ICA), and the situation returned to normal at 1.30pm.
The ICA said the disruption resulted in "intermittent slowness" in the system for cars.
However, "the automated clearance system as well as clearance systems at the motorcycle and bus zones were not affected", it said in a statement.
The system at the affected lanes progressively resumed normal operation from 8am, according to the ICA.
But checks by The Straits Times of traffic webcams around noon showed long lines of vehicles in both directions. The traffic appeared to have eased for departures at about 1pm, but there was still a backlog of vehicles waiting to enter Singapore.
During the disruption, more resources were immediately deployed, with officers on the night shift remaining behind to assist in the clearance of travellers, the ICA said. One of the departure car zones was converted to clear arriving cars.
The authority said that at 11am, operations had to be temporarily suspended to secure a vehicle that evaded departure clearance at the Malaysia checkpoint.
The ICA first warned about heavy traffic at Tuas Checkpoint at 7.24am. In an update at 7.45am, it said the delays were due to an intermittently slow clearance system. The timing of the power trip coincided with the morning peak period.
At 1.30pm, it said the system had returned to normal but traffic remained heavy.
Frustrated motorists turned to social media platforms to post pictures of the jam at Tuas, with some netizens complaining that they needed a toilet break.
Heavy traffic was also seen at Woodlands Checkpoint yesterday morning. At 10.45am, the ICA said the checkpoint was experiencing heavy departure traffic. This was because of heavy backflow of vehicles from Malaysia.