A police boat carrying armed officers has crashed near Westminster Bridge, police sources have said. RNLI responders have been observed treating casualties on a boat at Westminster Pier. A significant deployment of police officers, fire crews, and ambulances is on site, causing traffic across the bridge to come to a standstill.A Port of London Authority spokesperson said: “We are aware of an incident involving a police vessel at Westminster Bridge.“We are supporting the response and providing assistance where needed, working closely with the Metropolitan Police, HM Coastguard and partner agencies to manage the situation.”A police helicopter and an air ambulance were circling above.Entrances three and four to Westminster Underground station have been shut, Transport for London has confirmed.This is a breaking news story, more to follow... Subscribe here to get the latest updates from The Independent