Lindsey Vonn was airlifted to a hospital after a serious crash. Reuters

American Lindsey Vonn suffered a serious crash in the women's super-G on the opening day of the alpine skiing world championships on Tuesday.

A helicopter was called to take the four-times overall World Cup champion to hospital.

The race had been delayed by fog and commentators queried whether it should have even started with shadows beginning to form.

The race resumed after Vonn was helped from the piste but top skiers Maria Hoefl-Riesch and Anna Fenninger immediately made mistakes to also drop out.

Vonn had tumbled on the piste halfway down in a race which started three-and-a-half hours behind schedule given the poor visibility.

Vonn hurt her right knee as she nearly somersaulted on the snow and was heard screaming in pain on the side of the course.

Slovenia's Tina Maze, the runaway World Cup leader, was leading when the crash interrupted the race and she stared in horror as her arch-rival hit the ground.