Police were called at 22:33 BST on Wednesday to report of a man injuring people with a knife.
One of the victims, a woman in her 60s, was treated at the scene but was pronounced dead a short time later.
A 19-year-old man was arrested at 22:39 after a Taser was discharged by an officer. The Met said mental health was a "significant factor" in the events.
Two other women and three men received various injuries in the attack, Scotland Yard confirmed later.
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