Five Metropolitan Police officers have been injured after a police boat struck Westminster Bridge in central London.
Armed officers from the Marine Policing Unit were involved in the incident, which the Met said occurred at about 15:40 BST on Friday.
One officer has since been discharged from hospital and the others have serious but non-life-threatening injuries.
The Marine Accident Investigation Branch is leading an investigation into the crash.
The police confirmed that no members of the public were involved or injured in the crash.
The police boat was responding to a report of a person in the water near Battersea.
The Met said in a statement: "As a result of the collision, three officers were thrown from the boat into the water. They were recovered by those on nearby boats.
"Additional officers responded alongside the London Ambulance Service and London Fire Brigade."
The Met's Cmdr Nick John thanked river users "who came to the aid of the officers, as well as other police and emergency service colleagues who immediately made their way to the scene to assist".
He added: "The quick-thinking and professionalism of all those involved undoubtedly prevented any further injuries."
Mother and son Cecilia Lusevic, 56, and Mateo Bilis-Lusevic, 12, said they heard a loud bang when the police boat crashed into Westminster Bridge and then watched as the officers were rescued from the River Thames.
The visitors from Chile were on a river tour boat on the north side of the central London bridge when they saw the incident. They were evacuated from their vessel shortly after.
Mateo said: "Two boats were riding extremely fast through the water.
"Suddenly, I heard a boom. I was looking towards the boat, and I heard a boom.
"Then three people went flying into the water and one of the people was really hurt."
He said the officers were in the water for about 10 minutes and a life ring was thrown for one of them.
A black rigid inflatable boat arrived to help them out of the water – the same boat that witnesses said they saw paramedics treating the casualties aboard.
Mateo said emergency services then also arrived.
A London Ambulance Service spokesperson said it sent ambulance crews, incident response officers, and paramedic teams as well as London's Air Ambulance to the incident.
London Fire Brigade said it deployed a fire boat and three fire rescue units with water rescue capabilities to the scene.
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