NEW Zealand's sheep are the butt of jokes overseas, but a woman on the nation's North Island has found they can also be dangerous.

The woman was taken to hospital after suffering serious leg injuries in a sheep stampede while she was trying to muster a mob on a farm near Pongaroa, about 100km east of Palmerston North, today.

Palmerston North Rescue Helicopter pilot Chris Moody said the sheep trampled the woman's leg after she was knocked down.

She was taken on the back of a ute to the helicopter before being flown to Palmerston North Hospital.

A hospital spokesman said the woman, aged in her 50s, was in a stable condition.