Five cars - understood to be Singapore vehicles - and a Malaysia-registered bus were involved in an accident at the Woodlands Checkpoint yesterday morning.
The Singapore Civil Defence Force (SCDF) was alerted to the accident at 4.30am, it said.
A woman in her 60s and a man in his 50s were taken to Khoo Teck Puat Hospital. A teenage couple declined to be taken to hospital.
Photos posted on Malaysian Facebook pages showed that at least one car was badly damaged.
A blue bus with a Malaysian licence plate had ended up on a kerb.
The Straits Times understands that the bus driver claimed that his brake malfunctioned, leading to the crash.
There were more than 10 passengers on the bus but they were unhurt.
The SCDF sent two ambulances to the scene. Police investigations are ongoing.
Chew Hui Min