Four people were in Royal Perth Hospital last night after a motorcycle crash in Success yesterday.
Major Crash officers are investigating the crash that left two male motorcycle riders and their female passengers with serious injuries.
Police said a Harley Davidson motorcycle and a Yamaha motorcycle were travelling together heading west on Russell Road about 11.20am.
"At the same time, a Mazda CR-7 was travelling east on Russell Road intending to turn right on to the Freeway south entrance," a police spokeswoman said.
"The two motorcycles and the car entered the intersection – which is controlled by traffic lights – at the same time and collided.
"As a result of the crash, both riders of the motorcycles and their two pillion passengers received serious injuries and were taken to Royal Perth Hospital."
Investigators have called for the public’s help to determine what happened in the lead-up to the crash.
The two male motorcycle riders were last night in serious but stable conditions in RPH.
Two women, who were pillion passengers, were also in RPH with less serious injuries.
The female driver of the car was treated for minor injuries.
Russell Road bridge was closed for four hours yesterday while investigators inspected the scene.
Major Crash would like to speak to anyone who saw the crash or the Mazda or motorcycles before the crash.
Anyone with any information about the incident is urged to call Crime Stoppers on 1800 333 000.