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By Alex Johnson

A man was in custody Wednesday night after he went on a rampage with a knife in central London, killing a woman and injuring five other people in what police said was a possible terrorist attack.

The suspect was described as a 19-year-old man who was under police guard in a hospital.

The wounded were three men and two women. No details on their conditions were immediately available.

Police at the scene of a fatal knife attack Wednesday night in Russell Square in central London.ITN

The Metropolitan Police said the man was arrested about 10:40 p.m. (5:40 p.m. ET) after he was brought down with a Taser in Russell Square, near the British Museum.

"Terrorism is one possibility being explored at this stage," police said, adding later: "Early indications are that mental health is a significant factor."

"However we are keeping an open mind regarding the motive and terrorism remains one line of inquiry being explored," Metropolitan Police Assistant Commissioner Mark Rowley added.

Rowley said Londoners would wake up Thursday to a noticeably increased police presence as what he called a precautionary measure.

One of the July 7, 2005, bombings, which killed 52 people in London, was on a bus in Tavistock Square, near Russell Square, which is home to an annual commemoration of the attacks.