On Buckingham Palace Road, where the rider was thrown to the ground, first responders were seen treating someone in the street behind a blue tarpaulin.
One cab driver, identified only as Robbie, told U.K. public broadcaster the BBC 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 was his two passengers in the back. “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 that “it looked like it was injured quite badly.”
It’s not clear why or how the horses escaped, but one of the areas in which they were seen is patrolled by the Household Guards, an elite army mounted unit that takes part in the king’s birthday and other ceremonial parades.
The distinctive helmet, adorned with plume of horses hair, will be familiar to anyone who watches Britain’s opulent royal events. The mounted riders also don a piece of metal chest armor and carry swords.