A car crashed into a railing near The Roti Prata House in Upper Thomson Road at about 6.15 pm on Sunday.
Four people - the driver and passenger in the car, both women, and two men - were injured and taken to Tan Tock Seng Hospital. One of the men was in his 30s, while the other victims were in their 20s.
The Singapore Civil Defence Force said the driver suffered abrasions on her right thumb, while the passenger had said she felt pain in her left shoulder.
The men had cuts on their foreheads, believed to be due to flying debris that hit them.
All four people have since been discharged.
Mr Syed Ridzwan, 39, was working at The Roti Prata House when the accident happened.
He told The Straits Times that the two men with cuts were diners at his restaurant and, for one of them, "the injury was quite bad".
There were about 80 customers then, and after hearing a loud bang, some customers rushed out to see what had happened, he said.
The driver is believed to have been making an illegal U-turn when she hit Mr Ridzwan's friend's car and lost control. She was trying to avoid a bus nearby when she hit the railing, he added.
Another restaurant worker told Chinese daily Lianhe Zaobao that a church nearby typically has activities on Sunday nights till about 7 pm, and churchgoers would usually be waiting at the bus stop after the activities.
He said that, thankfully, there were few people at the bus stop then; otherwise more people could have been hurt. Police said investigations are ongoing.