Woman stabbed to death and five injured in London knife attack as police probe terror link
* A woman in her 60s has died in a knife attack in Russell Square, in central London
* Four men and a woman have been injured
* Metropolitan police said mental health a significant factor attack
* Terrorism is also one possibility being explored
* 19-year-old suspect currently in hospital in police custody
A 19-year-old man has been arrested on suspicion of murder after a knife attack in central London in which a woman was killed and five other people injured.
Counter-terrorism officers are supporting the investigation into the incident, while Scotland Yard said early indications suggest mental health "was a factor".
Armed officers raced to the scene in Russell Square on Wednesday night following reports that a man armed with a knife was targeting people.
A woman, believed to have been in her 60s, was pronounced dead at the scene, while two other women and three men were hurt.
As a result of the attack armed police and other officers will be deployed on the streets of London on Thursday as a "precautionary measure" to A Taser was discharged during the arrest of the suspect.He received hospital treatment and was then taken into custody at a police station in south London.
The Metropolitan Police's Homicide and Major Crime Command is leading the investigation, supported by counter-terrorism officers.
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."
In an earlier statement, police said terrorism was "one line of inquiry being explored".
#London Russell Square locked down & surrounded with police officers. Many police cars & ambulances.— Abdulrahman Muammar (@Am3mr) August 4, 2016
Eyewitness Zuhair Awartani told the BBC he saw the attacker being arrested.
He said: "I arrived here at my hotel and I saw the guy getting arrested just on the block.
"There were two police cars and he was like African ... a dark-skinned man ... late 20s probably.
"We heard that there'd been stabbing going on. The streets were blocked and no-one was allowed through."
The attack came hours after Scotland Yard announced that more armed officers would be deployed on public patrol around the capital.
Security services are on high alert following a spate of terrorist incidents around Europe. The official threat level from international terrorism currently stands at severe - indicating that an attack is highly likely.
On Sunday, Metropolitan Police Commissioner Sir Bernard Hogan-Howe warned that a terror attack in the UK was a case of "when, not if".
There have been warnings that Islamic State may be targeting people with mental health problems to inspire them to perpetrate attacks.
Police were called to Russell Square, a popular tourist area near the British Museum in Bloomsbury, shortly after 10.30pm on Wednesday to reports of a man armed with a knife assaulting people.
A Met spokesman said: "Numerous other calls were made by members of the public between 22.30 and 23.00hrs with reports of a man attacking people with a knife between Russell Square, Montague Street, Bloomsbury Square and Great Russell Street."
Armed officers attended the scene within around five minutes of receiving the first call. A Taser was discharged as the suspect was held, while no shots were fired.
Two women and three men suffered "various injuries", police said.
Two of the five are still in hospital but no details of their conditions have been released so far. The others have been discharged.
A cyclist passing the scene moments after the stabbing was stopped by a Spanish family who flagged him down for help.
Fernando, 40, from Brazil, said he was the first to call the ambulance and saw an "older woman" slumped against the railings with a stab wound to her back, an Englishman with an injury to his upper chest, and a younger girl with a wound on her upper arm.
He said: "I was just cycling by when I saw that. The Spanish family just stopped me, just asked me 'Call someone, call an ambulance'.
"There were three people stabbed. The older woman was slumping against the gates, and it was another two people. One of the Spanish family was comforting the older woman.
"I thought they were friends, but then I realised that they were just passing. No-one knew each other."
He added that he had not seen the attacker but said the Spanish family told police the man was wearing black shorts and a white shirt, and was covering his face as he made sweeping, stabbing motions.
Fernando went on: "The moment the police arrived, they asked them if the man had been shouting.
"They said that he didn't say anything. They said that when he stabbed the people he didn't shout or scream anything."