Police say they cannot rule out "terrorism as a motivation" after a woman in her sixties was killed and five people were injured in a mass stabbing in Russell Square, and warned Londoners will wake up to an increased police presence on the streets of the capital on Thursday.
The Metropolitan Police said more officers were being deployed as a "precautionary measure" to provide reassurance, but the public were urged to remain "calm, vigilant and alert".
The incident is being investigated by the Met's homicide command with the support of counter terrorism police.
Speaking outside Scotland Yard in the early hours of Thursday morning, Commander Mark Rowley said it had been a "tragic incident".
He said: "Police were called just after 10.30pm last night to reports of a man, armed with a knife, assaulting people in Russell Square, Camden.
"Armed officers arrived at the scene within five minutes, they discharged the Taser whilst confronting and arresting the suspect.
"Six people have been injured, including the one woman who sadly died at the scene, and the others have received various injuries."
Mr Rowley said the dead woman was in her 60s, but it was "inappropriate at this time to give any more personal details about her".
A 19-year-old man was arrested a shortly after 10.39pm and is currently in police custody at hospital, he added.
Mr Rowley said: "Early indications suggest that mental health is a significant factor in this case and that is one major line of inquiry.
"But of course at this stage we should keep an open mind regarding motive and, consequently, terrorism as a motivation remains but one line of enquiry for us to explore."
Additional reporting by agencies
