Mayor of London Sadiq Khan is urging all Londoners to "remain calm and vigilant" after a woman was killed and five others injured following a mass stabbing in Russell Square. A 19-year-old male suspect has been arrested by police following the attack in central London in which a woman in her 60s was killed and two other women and three men receiving various injuries.

Armed officers attended the scene within five minutes of receiving reports of a man attacking people with a knife just after 10:30pm on 3 June and detained the suspect after discharging a Taser.

The incident is being investigated by the Metropolitan Police Service's Homicide and Major Crime Command with support by officers from the Counter Terrorism Command. Police said while terrorism remains one line of inquiry, early indications "suggest that mental health is a significant factor" in the case.

Police have deployed firearms officers to the area and the usually busy area of central London has been closed off to the public while investigations continue.

One eyewitness told BBC Radio 4's Today programme: "We saw a guy being lifted into a stretcher and we didn't realise just how bad it had been because a lot of people got hurt, it wasn't just that one guy. As we made our way around the corner, we saw the guy [suspect] on the ground and they had taped him off in a triangle. They left him on the ground for a while then as we were watching they slowly went over the put the handcuffs on."

Russell Square Knife Attack Woman Killed
A police forensic officer works in Russell Square after a knife attack in which a woman in her 60s was killed and five others injured JUSTIN TALLIS/AFP/Getty Images

The Mayor of London has now reassured that "the safety of all Londoners is my number one priority" and paid respect to the victims of the incident.

Khan added: "I have spoken with the Commissioner, and the Assistant Commissioner, who have assured me that our police officers are working extremely hard to investigate exactly what has happened and to keep the rest of us safe. A man was arrested at the scene. Police have spoken to him and are seeking to establish the full facts including motives for this attack.

"I urge all Londoners to remain calm and vigilant. Please report anything suspicious to the policeā€Ž. We all have a vital role to play as eyes and ears for our police and security services and in helping to ensure London is protected. Our police officers are doing an incredibly difficult job on our behalf and they have my full support."

Sadiq Khan
Sadiq Khan has urged the public to remain 'calm and vigilant' as police investigate Leon Neal/ AFP

Assistant Commissioner Mark Rowley, from the Metropolitan Police, 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 and terrorism remains one line of inquiry being explored.

"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 incident occurred after Met Police announced they would be deploying 600 more firearms officers to patrol the streets of London following the recent terror attacks across. Announcing the decision, Met Police Commissioner Sir Bernard Hogan-Howe said: "Anyone who's been following events in Europe over the past few weeks will understand why we want to show our determination to protect the public. We are deadly serious about the protection that we are offering the people of London and we will never be complacent."

Update: Police confirm a 19-year-old male has been arrested on suspicion of murder following his release from hospital and is currently in custody at a south London police station. Two of the injured victims remain in hospital while the other three have been discharged.