A man has been arrested on suspicion of murder after a woman was killed and five others injured in a stabbing attack in Russell Square.
The female victim, believed to be in her 60s, was pronounced dead at the scene in central London on Wednesday night.
Police received their first call just after 10.30pm with reports a man armed with a knife was assaulting people.
A spokesperson for the Metropolitan Police said members of the public made "numerous" calls for the next half an hour saying a man was attacking people with a knife between Russell Square, Montague Street, Bloomsbury Square and Great Russell Street.
Armed officers and paramedics arrived within minutes but could not save the woman. The 19-year-old suspect was restrained using a Taser and arrested.
After receiving treatment at hospital he was taken into custody at a police station in south London.
Two women and three men were injured in the attack. Two of the victims remain in hospital, while three others have been discharged.
Investigators have not confirmed any link with terrorism and said they were pursuing lines of inquiry on mental illness while retaining an "open mind" regarding the motive.
Assistant Commissioner Mark Rowley said: “This was a tragic incident resulting in the death of one woman and five others being injured. Early indications suggest that mental health was a factor in this horrific attack. However we are keeping an open mind regarding the motive.
“As a precautionary measure, Londoners will wake up this morning to notice an increased presence on the streets of officers, including armed officers today. We would urge the public to remain calm, alert and vigilant.”
The Metropolitan Police Service's Homicide and Major Crime Command is leading the investigation, supported by officers from the Counter Terrorism Command.Anyone with information is asked to contact the incident room at Lewisham police station on 020 8721 4868 or if they wish to remain anonymous, Crimestoppers on 0800 555 111.