Metropolitan Police Commander Nick John said of the bridge collision: "Our thoughts are with all those involved, in particular our officers who were injured and those who responded in challenging circumstances.

"The four officers who remain in hospital have serious but non-life-threatening injuries. We will give them all every support as they recover.

"I must also offer our thanks to those 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.

"The quick-thinking and professionalism of all those involved undoubtedly prevented any further injuries."

An update issued by Met Police states that the boat, which is owned by the force, was responding to reports of a person in the water further up the river.

Three officers were thrown into the River Thames by the collision before they were rescued by those on nearby boats.

In a statement, the force said: "At around 3.40pm on Friday, 24 July, a boat from the Met’s marine policing unit struck Westminster Bridge while responding to a report of a person in the water near Battersea.

"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.

"Five officers were injured and received treatment at the scene before being taken to hospital. One has since been discharged."

No members of the public were injured in the incident, the Met added.

Westminster Bridge has now reopened, with traffic and members of the public allowed to cross the bridge again.

A couple from the United States said they heard "an explosion" when a police boat travelling at "high speed" struck Westminster Bridge on the River Thames today, injuring five officers.

Jim Bagley, from Gloucester, Massachusetts, told the Press Association: "We were standing in line to get onto the city cruise hop on, hop off tours, and we saw two police boats coming up the river.

"One was an orange boat that went under the bridge and left a great big wave, and then there was a black boat that came up behind it, the police boat.

"It looks to me that he got stuck in the wake of the other boat that had just passed through the bridge and slammed into the wall on the opposite side.

"We didn’t see it happen, but we heard the explosion… the next thing we saw was three people in the water, coming down the river."

He added: "We were wondering why they were under way at high speed to begin with."

Katherine Bagley said: "They were both in pursuit of something farther down the river, but they never… the second boat never got to it because it crashed into the bridge with a big bang."

A fire service boat could be seen towing a police boat down the River Thames away from Westminster Bridge where five police police officers were injured in a crash this afternoon.

The black rigid inflatable police boat was tethered to the larger fire service vessel as it made its way down the central London river.

A witness said the boat that crashed into Westminster Bridge in central London sounded like a "car crash".

Enno, a 19-year-old German tourist who wished to keep his last name private, said he was walking over the nearby Hungerford Bridge when he heard a "crashing sound".

He added: "A black boat had crashed into the side of the bridge by the pier. I think around five police officers were in the water, at the same time.

"They looked hurt."

He said that emergency services then rushed to the scene and urged people to "stay away".

He added: "It sounded like a car crash from around 10 metres away.

"I had seen the black boat pass under the bridge and once I heard the sound, I saw that it had crashed."

An Uber Boat service, operated by Thames Clippers, has been cancelled and others delayed following this afternoon's police boat crash.

The RB1 3.26pm Battersea Power Station to Barking Riverside service was cancelled, the company said.

An Uber Boat by Thames Clippers’ spokesperson said: "An incident occurred in the vicinity of Westminster Bridge on Friday afternoon that did not involve Uber Boat by Thames Clippers, however some services may be subject to disruption or delay as a result.

"For further information and updates please refer to the Port of London Authority or the Metropolitan Police."

Westminster Bridge is now fully closed.

A police cordon blocks access at either end of the bridge near the Houses of Parliament, with buses operating on diversion routes.

Below are more pictures from the scene in Westminster showing a host of emergency services in attendance, from police cars and ambulances to fire engines.

(Image: AFP via Getty Images)

(Image: AFP via Getty Images)

A video taken by the Press Association shows the large-scale response deployed to Westminster this afternoon after a police boat crashed into Westminster Bridge.

A police cordon, numerous police vehicles and ambulances and a helicopter can all be seen at the scene.

London Fire Brigade has now also issued a statement on its response to this afternoon's incident at Westminster Bridge in central London.

It reads: "We're responding to an incident on the River Thames near Westminster Bridge alongside partner agencies.

"The Brigade's fire boat and three fire rescue units with water rescue capabilities, have been mobilised to the scene.

"We were called at 15:58 and remain on scene."

The incident took place as a police boat carrying armed officers crashed near Westminster Bridge on the River Thames.

Westminster Bridge is located in one of London's biggest tourist hotspots, with attractions like the Palace of Westminster, Big Ben, the London Eye and Westminster Abbey all within view of the bridge.

Other locations popular with tourists not too far from the bridge include St James's Park, Buckingham Palace and the National Gallery, with 10 Downing Street also only a few minutes away.

A spokesperson for the Met said: "At around 3.45pm on Friday July 24 a boat from the Met’s Marine Policing Unit struck Westminster Bridge.

"A number of officers entered the water but were recovered.

"Additional officers responded alongside the London Ambulance Service and London Fire Brigade.

"We understand five officers were injured and are receiving treatment. We await an update on the extent of their injuries.

"At this stage, we don’t believe any members of the public were involved or injured.

"The circumstances of the incident will be thoroughly reviewed, but at this stage our priority is the wellbeing of the officers involved."

A section of Westminster Bridge has been taped off by police officers following the boat crash on the River Thames.

A number of ambulances, fire crews and police vehicles are in attendance along Embankment, with a helicopter also circling overhead.

Five police officers have been injured after a police vessel hit Westminster Bridge, the Metropolitan Police has said.

A number of officers had to be recovered from the River Thames, the force said.

A large number of police officers, fire crews and ambulance staff are at the scene(Image: David Lynch/PA Wire)