Four people were taken to hospital after spooked army horses broke loose during morning exercises in central London and galloped through the streets at rush hour, the army and emergency services said.

Warning: this story contains images that some readers may find distressing.

Photos and video posted on social media and by British news outlets showed the horses running along busy roads, dodging buses, taxis and other traffic.

Both were wearing saddles and bridles, with one apparently covered in blood on its chest and forelegs.

London's Metropolitan Police said it was "working with colleagues in the army to locate them".

A number of prestigious army regiments have stables in the British capital and horses are a regular sight around government buildings on Whitehall, Buckingham Palace, The Mall and in nearby Hyde Park.

The London Ambulance Service was called at 8:25am (local time) to reports of a person being thrown from a horse on Buckingham Palace Road in central London, a spokesperson for the service said.

No details were released on the injured people or the exact circumstances of their injuries.

The driver of a Mercedes car told LBC radio he had been waiting outside a hotel in Buckingham Palace Road when he felt something smash into his car.

He said he saw three or four horses near the vehicle, and that an army rider had been thrown off and injured.

One horse also reportedly crashed into a parked double-decker tour bus, smashing the windscreen.

Up to seven horses initially got loose, Britain's domestic Press Association news agency reported, with police working with the army to recapture them.

The army said in a statement that "a number of military working horses became loose during routine exercise this morning".

Two of the horses were recaptured by the City of London Police, which polices the Square Mile financial district.

It said officers had contained two animals and that "an army horse box had collected the horses and transported them to veterinary care".

AFP