Canada's Summer McIntosh wins Olympic women's 400m medley gold

Canadian prodigy Summer McIntosh won a maiden Olympic gold medal Monday with a dominant 400m medley swim, clocking the fourth-fastest time ever to reinforce her burgeoning reputation.

The 17-year-old world record holder powered to the wall in 4mins 27.71secs, outpacing American pair Katie Grimes (4:33.40) and Emma Weyant (4:34.93).

It was the Toronto swimmer's second Paris medal after pipping Katie Ledecky to win silver behind Australian star Ariarne Titmus in the 400m freestyle.

She is also favourite in the 200m medley and a serious contender in the 200m butterfly as she hovers on the edge of superstardom.

McIntosh, who made her Olympic debut at Tokyo as a 14-year-old, was the clear favourite after lowering her own world record in May when she clocked 4:24.38 at the Canadian trials.

She went out hard in the opening butterfly leg and extended her lead through the backstroke ahead of Grimes.

Breaststroke is her weakest stroke, but she never let up and brought home the gold with cracking freestyle swim.

She now owns three of the four fastest times in history.