Reports suggest a man went into a shop on the busy high street with a knife and started stabbing people.
It appears the man then left the shop and stabbed a woman, possibly a cyclist.
It seems police were then on the scene.
Witnesses report hearing three gun shots and a man was seen lying on the floor, as armed police approached.
The London Ambulance Service said it was treating a number of people at the scene.
The Metropolitan Police said it was awaiting updates on the condition of those injured.
A large police cordon stretches from Streatham Hill station and there is a heavy police presence; helicopters are overhead.
One eye witness told how he saw the shooting take place in front of a Boots pharmacy.
“I was crossing the road when I saw a man with a machete and silver canisters on his chest being chased by what I assume was an undercover police officer,” he told the PA news agency.
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