Teenager held after woman killed and five injured in central London knife attack

Counter-terrorism officers are supporting the investigation into the attack, although Scotland Yard said it was focusing its lines of inquiry on mental health.

Armed police raced to Russell Square, a popular tourist area near the British Museum in Bloomsbury, shortly after 10.30pm on Wednesday after reports of a man armed with a knife assaulting 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.

A Taser was discharged during the arrest of the suspect, who received hospital treatment and was then taken into custody at a police station in south London.

On Thursday, a cyclist who was passing the scene moments after the stabbing, told how he was flagged down for help by a Spanish family.

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 English man 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."

He added that the Spanish family had described the attacker as a "chubby-faced" white man.

A heavy police presence and cordon remained in place on Thursday morning, with a forensics tent marking the spot where the woman, who has not been identified, was killed.

A private ambulance was seen removing the body at around 5.20am.

The London Ambulance Service (LAS) said paramedics gave the woman "extensive treatment" at the scene but she could not be saved.

Pol O'Geibheannigh, 45, was walking back from the cinema when he saw a massive police presence and a woman lying in a pool of blood.

He said: "I just knew right away that this is not right. You just don't see armed police around this area.

"This was just wall to wall with armed police. You could see a woman on the floor. She was lying in a pool of blood with a red blanket on top of her. I went into the bar and it wasn't until an hour later that they put the tent up.

"And then at about 12.30, when we were coming out, there were about five or six people running off towards Bedford Square.

"That level of police presence I haven't seen since 7/7 and I was here - I live around the corner."

Police were first called to Russell Square just after 10.30pm on Wednesday.

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.

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."

Police had initially said terrorism was "one line of inquiry being explored" but this reference was not included in the most recent statement.

The attack came hours after Scotland Yard announced that more armed officers would be deployed on public patrol around the capital.

London Mayor Sadiq Khan called for the public to remain "calm and vigilant".

He said: "The safety of all Londoners is my number one priority and my heart goes out to the victims of the incident in Russell Square and their loved ones."

The events on Wednesday night unfolded close to Tavistock Square - the scene of the bus bombing during the July 7 attacks in 2005.

Met Police Commissioner Sir Bernard Hogan-Howe vowed to protect the capital, adding: "A normal night out in our busy capital has ended in horrific circumstances."

He said: "My thoughts are with the family of the woman who was murdered and those who were injured."

The investigation is "moving very quickly", Sir Bernard said.

He went on: "As we have already made clear, mental health remains a substantial focus for our investigation.

"Every day in London, my officers patrol and carry out operations to catch criminals in the knowledge that they face risk and danger.

"I am proud that last night our specialist firearms officers were on the scene in six minutes and, using only a Taser, detained the subject. That demonstrates our commitment to use force in a professional and proportionate way.

"Their swift response undoubtedly helped to prevent more people from getting injured."

Earlier on Wednesday, Scotland Yard announced that the first of the force's additional 600 marksmen, put in place following terror attacks in mainland Europe, are trained and operationally ready.

Officers armed with handguns and semi-automatic weapons, as well as Tasers, will go on routine patrol in the capital.

Sir Bernard said: "Across our capital today you will see more police officers, armed and unarmed, to reassure the public after recent events overseas.

"We will protect our capital and those who live, work and visit our city."

In a speech in Dagenham, Labour leader Jeremy Corbyn said: "We should express our sympathies to the family of the poor woman who was stabbed to death last night in Russell Square and thank the police for the action they took very quickly to make the area safe. This is an appalling event that happened.

"I would urge no-one to speculate on the reasons or the causes for it, but to be grateful that we have efficient emergency services that were able to bring about some safety for that area at the present time."