British police said they arrested a man after a stabbing in London's Leicester Square, which was not being treated as a terrorist incident, and that an 11-year-old girl and a 34-year-old woman had been taken to hospital.

Britain's police forces remain on high alert after days of riots earlier this month, triggered by false online posts wrongly identifying the suspected killer of three girls in northern England as an Islamist migrant.

The police said they didn't believe there were any outstanding suspects from the attack in Leicester Square, an area in the centre of London which is popular with tourists.

A spokesperson for the London Ambulance Service said the victims had been taken to a major trauma centre after ambulances and response units arrived to reports of a stabbing at 1036 GMT.

"We await an update on their condition," the police said.