An American woman in her 60s was killed and five others injured in a knife attack in central London's Russell Square in what police Thursday called a "spontaneous" assault.The stabbings late Wednesday night rattled the city popular with tourists and came just hours after authorities announced an increased police presence there following recent terror attacks 

"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," Rowley told journalists.

Police said two other women and three men were injured. The victims were from Britain, Israel, Australia and the United States.

An earlier police statement said two remained hospitalized. 

Dying in family's arms

Police were called after 10:30 p.m. Wednesday following reports of a man "seen in possession of a knife injuring people," authorities said in a statement.

Officers used a stun gun on the suspect, and he was arrested less than 10 minutes later, authorities said.

He was treated in the hospital and is in police custody at a south London station, police said.

A 40-year-old Brazilian man living in London told CNN a Spanish family stopped and asked him to call an ambulance on Wednesday night. 

 

"I thought someone had collapsed or passed out, that was my first impression," said Fernando, who did not want to give his last name. 

He said one of those family members was holding the dying woman and helping and reassuring her. She had been stabbed in the back, Fernando said, adding that he was in shock.

"It was not nice to see someone dying," he said.

Philippa Baglee told CNN she saw the aftermath of the attack.

"I came out of the Atrium (bar) to have a cigarette, and I saw people standing over there looking at the ground. I could see someone laying down and a guy with a motorbike helmet balanced on his head just walking up and down," she said.

Janet Pavely, who was with Baglee, said people had to be "very self-aware" when out in public now.

"It could happen anywhere. I don't think it would stop us from coming back. We were lucky last night. We were going to walk, we took a cab instead. Who knows?" she said.

A woman lays flowers at the scene of the knife attack in London's Russell Square on Thursday.

Police were lifting cordons around the crime scene by late Thursday morning. Workers sprayed and scrubbed the sidewalks clean as people began to leave flowers at the site.

Police presence beefed up

Londoners woke up Thursday to a heavier police presence on their streets after the attack in the heart of the city.

Rowley said it was "to provide reassurance and safety. We ask the public to remain calm, vigilant and alert."

London Mayor Sadiq Khan also urged residents to stay calm and on the alert following the attack.

"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," Khan said in a statement from his press office.