Update. BBC World reports that Scotland Yard says this is, thankfully, a road traffic accident. 11 people were injured, but no fatalities.
I'm not in the country at the moment but this is breaking news from London, my home, this afternoon. From the Telegraph.
A man has been arrested after a car mounted the pavement outside the Natural History Museum in London, hitting a number of people. It is understood the car mounted the pavement as visitors made their way to the museum, in west London, before ploughing into two other vehicles.
A man was seen shortly after being held to the ground by security guards.Photographs showed at least four police cars and a number of ambulances parked on Exhibition Road, outside the museum, as officers dealt with the incident.
Scotland Yard said in a statement - ". . A man has been arrested at the scene. Enquiries to establish the circumstances and motive are underway. If you have any information about this incident, please call 101."
Reports suggested the black Toyota Prius which mounted the pavement was a licenced taxi cab.
The Natural History Museum, especially on a Saturday or Sunday is a favourite place to take children who adore the dinosaurs. If this is a deliberate attack, for any motive, targeting children is a particular low.