Gwangju - American teenager Regan Smith smashed the women's 200 metres backstroke world record Friday, lopping a huge chunk off countrywoman Missy Franklin's old mark.

The 17-year-old stormed to victory in the second semi-final in Gwangju, firing off a time of two minutes, 3.35 seconds - a whopping 0.71 faster than Franklin swam at the 2012 London Olympics.