A policeman was injured after an attempted moped robbery at Brent Cross shopping centre.
Six raiders riding on three bikes targeted a watch shop in the north London complex at around 7pm on Tuesday, Scotland Yard said.
Two men were arrested on suspicion of conspiracy to rob. Four other suspects fled on two motorcycles.
An officer was taken to hospital with a head injury, which is not believed to be serious.
A woman in her 50s was treated by paramedics for an injury to her arm.
A Metropolitan Police spokesman said: "Urgent inquiries are under way to trace them.
"We await confirmation of whether anything was stolen."
One of the suspects was taken to hospital for minor injuries and the other is in custody in a north London police station.
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