London: An American woman was murdered and an Australian was among those injured in a mass stabbing attack in central London, UK police have revealed.

Scotland Yard said two women and three men from different countries including: Australia, America, Israel and Britain were injured in the incident. None were said to have life-threatening injuries.

A Norwegian of Somali origin was arrested and interviewed after initially being taken to hospital for treatment.

Police raided the man's house in north London and plan to search another address in south London.

Police have all but ruled out terrorism as a factor and said they were exploring mental health issues as a motivating factor instead.

Assistant Commissioner Mark Rowley told reporters police believed the attack was "spontaneous" and the victims "selected at random".

"So far we have found no evidence of radicalisation or anything that would suggest the man in our custody was motivated by terrorism," he said.

"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," he said.

The stabbing took place near the British Museum between Russell Square, Montague Street, Bloomsbury Square and Great Russell Street.

Police were called at 10.30pm and say they were at the scene within six minutes. They tasered the 19-year old suspect and said at no point were any shots fired.

Assistant Commissioner Rowley praised police and said it was a testament to the British philosophy of using minimum force.

"Our firearms officers bravely rushed to that scene with very little information.

"They would not have known if this was an act of terrorism or the random attack we now know it be.

"We should be proud of them and the British tradition of using the minimum necessary force," he said.

The attack came on the same day UK Police announced they would be deploying 600 extra armed officers to man the streets of central London in the wake of the sporadic terror attacks across Europe, with police warning a similar attack in the British capital was all but inevitable.

The Mayor of London Sadiq Khan issued a statement and said the safety of Londoners was his "number one priority."

"I urge all Londoners to remain calm and vigilant. Please report anything suspicious to the police‎. 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.

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