A Traffic Police officer and a paramedic attending to accidents were injured on Sunday after another car skidded while they were at the scene.
Six other people were also injured and all were taken to hospital.
A police statement on Sunday said the first accident involving two cars and a tipper truck took place at about 11.15am along the Pan-Island Expressway towards the direction of Changi Airport, before the Bukit Timah Expressway exit.
Two motorcyclists also skidded at the location in separate accidents, the police said.
After the Traffic Police and Singapore Civil Defence Force (SCDF) arrived at the accident scene, a third car skidded.
The car hit a 30-year-old Traffic Police officer and a 26-year-old SCDF paramedic, who were attending to the earlier accidents, as well as the two motorcyclists, aged 35 and 37, who were moving their bikes away to avoid obstructing traffic.
Four people aged between 25 and 69, who were involved in the accident between the tipper truck and two cars, were also indirectly injured by the impact.
All those taken to hospital were conscious, police said.
The 44-year-old driver of the third car has been arrested for a rash act causing grievous hurt.
Chinese-language newspaper Shin Min Daily News said the accidents resulted in a serious traffic jam, with cars backed up for 3km.
In the first accident, a silver car lost control and crashed into the tipper truck before slamming into a seven-seater multi-purpose vehicle, Shin Min reported.