Police and ambulance workers attended the scene on Wandsworth High Street on Tuesday evening
Officers cordoned off the high street for around two hours before letting traffic through again.
A spokesman for the Met Police said: "Police were called to Wandsworth High Street, SW18, shortly before 16.00hrs on Tuesday, 6 July to reports of a van in collision with two cyclists.
"Officers attended along with paramedics from the London Ambulance Service.
Wandsworth high street it is closed
Waiting for a update pic.twitter.com/hk2QfPCWLy— London & UK Crime.. (@CrimeLdn)July 7, 2020
"The cyclists, a man and a woman, were treated at the scene before being taken to hospital.
The spokesman added that the woman was seriously injured, but that the cyclists' lives were not in danger.
He went on: "The driver of the van stopped at the scene. Enquiries in to the circumstances continue."