A woman holding an infant was injured by a sign that came loose when a helicopter was practising its landing at the Summerside, P.E.I., waterfront Sunday before being used to transport Prince  William and Kate.

Rebecca Graves, 31, of London, Ont., suffered a non-displaced skull fracture and concussion, with possible jaw injuries, after being hit by the sign on the back of the head.

She fell with her 10-month-old baby in her arms; the infant was not seriously injured but sufferered a bloody nose and some scratches.

Her husband, Robert, told CBC News the family had come to the Island specifically to see the royal couple.

The family was watching the rehearsal of a CH-149 Cormorant helicopter landing when winds underneath the helicopter, which was to transport the royals on Monday, caused the sign to come loose and hit her on the head.

Robert said the family had a particular interest in the helicopter exercise because Rebecca's father was a helicopter pilot. He added she was disappointed she won't get to see the royals.

Rebecca needs facial surgery, so the family is deciding whether to go to Halifax or return to Ontario.

Summerside police said two other women — one from P.E.I. and one from Halifax — were hit by the flying sign, which ended up in the water. The condition of the other two women isn't known.

The incident happened around noon Sunday.

Capt. Scott Spurr, spokesman from the 413 Transport and Rescue Squadron based at 14-Wing Greenwood in Nova Scotia, described the incident as a "very rare/freak" accident .

The winds — called the downwash — can reach about 70 km/h.

Spurr said the military goes to great lengths to make sure that the area is clear and that spectators watch from a safe distance.

The pilots aborted the practice landing when they saw that the woman had been injured.

The landing was completed safely later in the day.