A woman in her 60s was killed by a man with a knife in Russell Square at around 10.30pm last night. Two other women and three men received various injuries in the attack, and three of the injured people have since been discharged from hospital.
Police were called at 10.33pm and a 19-year-old man was arrested at 10.39pm after a Taser was discharged by an officer. The suspect has been charged with murder.
The murdered woman was an American citizen, police have confirmed, while the injured people are Australian, American, Israeli and British.
The suspect is a Norwegian national of Somali ancestry, the police said.
"So far we have found no evidence of radicalisation or anything that would suggest the man in our custody was motivated by terrorism," said assistant commissioner Mark Rowley.
"Whilst the investigation is not yet complete - all of the work that we have done so far, increasingly points to this tragic incident as having been triggered by mental health issues.
"At this time we believe this was a spontaneous attack and the victims were selected at random."
Mayor of London Sadiq Khan today urged the public to remain "calm and vigilant" as police investigate the attack.
"The safety of all Londoners is my number one priority," Khan said.