First responders rushed to the scene and treated two people for injuries, the London Ambulance Service said. More paramedics were called to nearby Buckingham Palace Road, where another of the riders was thrown from a horse, it said. Crews there treated someone in the street behind a blue tarpaulin.

The horses galloped for miles. And another ambulance crew treated a horse-related injury at a busy junction not far from St. Paul’s Cathedral, it said. In total, three riders were injured and taken to hospitals with non-life-threatening injuries, according to the army.

It wasn’t clear exactly when the horses were brought under control, but by 10:30 a.m. the army said the animals had been contained and returned to camp.

Officials said some of the horses had been injured, although it was not clear what caused the large patch of blood that appeared to be splashed across the chest and front legs of one of them. The BBC sent a reporter to Limehouse, an area in the east of the city where at least some of the animals were retrieved, where they photographed a large patch of blood and horse manure on the sidewalk.

A cab driver, identified only as Robbie, told the U.K. public broadcaster he had heard “galloping and looked behind and there were about three or four horses.”

“I looked in the rear mirror and saw them coming right up behind me,” he added, saying his main concern were the two passengers in the back of his cab. “Luckily they swerved towards the middle of the road and carried on, but they were going at some speed.”

He described one of the horses as being “covered in blood” and said that “it looked like it was injured quite badly.”