Zara was taken to hospital as a precaution

The 23-year-old was competing in horse trials at Lulworth, Dorset, on Friday when the accident happened.

She was knocked out and taken to Dorchester Hospital where an X-ray revealed no broken bones. The horse was unharmed in the fall.

Buckingham Palace said she had been "given the all-clear and discharged."

Horse unsteady

Spectators saw Ms Phillips fall from her horse, Ardfield Magic Star, at the fourth fence.

Eyewitness Sheila Holt, from Ferndown, Dorset, described how Ms Phillips's horse was not obeying its rider as it approached the jump.

She said: "I think it was quite a nasty fall. She was doing jump number four and the horse would not be steadied, it just wasn't listening to her.

"They both landed on their heads and I think Zara was momentarily knocked unconscious and I think that is why she had to be carted off in an ambulance."

Buckingham Palace said: "Following a fall from her horse during a cross-country event in Dorset today, Zara Phillips was taken to Dorchester Hospital as a precautionary measure. It was not an emergency."