Last Updated Aug 4, 2016 7:05 AM EDT
LONDON -- Two people remained hospitalized Thursday after a 19-year-old man in possession of a knife killed one person and injured several at Russell Square in London late Wednesday night, Metropolitan Police said in a statement.
The man was under arrest on suspicion of murder.
Five people were injured in the attack that occurred around 10:30 p.m. local time on Wednesday. A female was treated at the scene, but was pronounced dead a short time later. 3 people were discharded from the hospital early on Thursday.
The deceased has been identified by police as a woman in her 60s.
The suspect was arrested just minutes after the attack, police said. A Taser was discharged by one of the arresting officers.
"Early indications suggest that mental health was a factor in this horrific attack," Assistant Commissioner Mark Rowley, from the Metropolitan Police, said. "However we are keeping an open mind regarding the motive."
Helen Edwards, 33, who lives in the area, came out for a walk and found armed police near a subway station. In a city where memories of the July 7, 2005, attacks on public transport remain raw, she immediately suspected that an attack had occurred.
"There is always that thing in the back of your mind," she said. "You live with that threat of terrorism or other crimes in the back of your mind. It wasn't a huge shock I guess."
London Mayor Sadiq Khan urged the public to keep calm and remain vigilant, urging people to be the first line of defense against any form of attack.
"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," he said.
The incident came within hours of an announcement by London police that they were putting more armed officers on the streets. The idea was to sustain public confidence following attacks by ISIS-inspired groups in Europe.
The move was important because police in Britain do not carry guns for the most part - a principle that remains unchanged. Even with the additional armed officers, most of London's 31,000 police officers will not be armed.
"In some of our big iconic locations, we've already got armed patrols - if you look at Parliament, Downing Street - so it's not entirely new," Metropolitan Police chief Bernard Hogan-Howe said Wednesday. "I think people understand that where you are going to have people as enemies who've got guns, we've got to have guns."
The deployments underscore the challenge police face in responding to situations in which they may be outgunned - or face a pressing need to subdue a suspect. Hogan-Howe warned over the weekend that an attack in Britain was a case of "when, not if."
Knives are the most common murder weapon in Britain, which has strict gun-control laws. There were 186 knife killings in the year to March 2015, according to government statistics - a third of all murders.
In the last three years London has seen two knife attacks by people inspired by radical Islam. In May 2013, two al-Qaida-inspired London men killed off-duty soldier Lee Rigby in the street near his barracks. In January, mentally ill Muhiddin Mire tried to behead a London Underground passenger, shouting that he was doing it "for Syria."