Princess Anne, the sister of King Charles III, has been hospitalised with a minor head injury and a concussion.

The 73-year-old daughter of Queen Elizabeth II was walking within her Gatcombe Park estate, about 170 kilometres west of London, when an incident occurred yesterday.

Exactly what happened is unknown but there were horses walking nearby and it’s believed her injuries are consistent with a potential impact from a horse’s head or legs.

Emergency services took her to hospital.

Princess Anne, Colonel-in-Chief of the Royal Regina Rifles, attends a ceremony to unveil a statue of a Second World War Canadian Royal Regina Rifleman to mark the 80th anniversary of D-Day, at Place des Canadiens in Bretteville-l’Orgueilleuse, Normandy, France on June 5. (Aaron Chown/Pool via AP)

“The Princess Royal has sustained minor injuries and concussion following an incident on the Gatcombe Park estate yesterday evening,” Buckingham Palace said in a statement.

“Her Royal Highness remains in Southmead Hospital, Bristol, as a precautionary measure for observation and is expected to make a full and swift recovery.

“The King has been kept closely informed and joins the whole royal family in sending his fondest love and well-wishes to the princess for a speedy recovery.”

Anne’s husband, Sir Tim Laurence, and children, Zara Tindall and Peter Phillips, were at the estate at the time.

The King and Queen Camilla and Anne’s other siblings were told of the incident last night.

Princess Anne and her husband Tim Lawrence ride in a carriage after attending the Order of the Garter service at St George’s Chapel at Windsor Castle on June 17. (AP Photo/Kirsty Wigglesworth, Pool)

Anne is regarded as one of the hardest working members of the royal family, attending dozens of official events throughout the year.

“On doctors’ advice, Her Royal Highness’s engagements for the week ahead will be postponed,” a palace spokesperson said.

“Her Royal Highness sends her apologies to any who may be inconvenienced or disappointed as a result.”

She was due to fly to Canada at the end of the week, however those plans are likely to be postponed.

Anne is the second of Elizabeth and Prince Philip’s four children and their only daughter.