A building has partially collapsed in Norbury, injuring two people.
The Metropolitan Police are advising motorists and pedestrians to stay away from London Road after the roof above Rage hairdressers fell in at about 11.45 am today.
A London Ambulance spokeswoman said one man suffered a head injury and was taken to St George's Hospital as a priority.
Another man went to Croydon Hospital with a foot injury.
The building has been declared unsafe and surrounding buildings have been evacuated.
A worker from Eva Hair and Beauty, opposite to where the building collapsed, said: "There were police, fire engines, ambulances - everything was here.
"Everything is closed now. It's very quiet. There's only the police and a few firemen.
"We were told to close and we thought we might be able to reopen this afternoon, but now we're going home."
A police spokesman said London Road was closed in both directions "and would be for some time".