Police and paramedics rushed to the scene of the incident in Anerley Road, Crystal Palace, shortly after 9.30am on Sunday.
An air ambulance also attended after a male motorcyclist, believed to be aged in his late 20s, collided with a car outside a petrol station.
He was rushed to hospital where he remains in a critical condition, a spokesman for the Met Police confirmed on Sunday evening.
The spokesman added: “No arrests have been made.
“The driver of the car involved stopped at the scene and is assisting police with their enquiries.
“He did not require hospital treatment.”
Part of the road was closed off while police officers carried out an investigation but it has since re-opened.
Anyone who witnessed this collision is asked to call police on 101 quoting CAD2315/25Feb.