Canadian Penny Oleksiak and Simone Manuel of the United States were inseparable at the finish and even more united in joy after a stunning 100 metres freestyle dead-heat rewarded both with Olympic gold on Thursday.

Both women, one 16 and the other 20, touched the wall in 52.70 seconds as the crowd gasped at the times flashing up on the scoreboard.

It was the second time the women's 100 freestyle had ended in such a fashion -- the 1984 Los Angeles Games saw a tie between Americans Nancy Hogshead and Carrie Steinseifer in 55.92.

That was the first double gold in Olympic swimming and it came after the timing was reduced from a thousandth of a second to a hundredth following a controversial dead-heat in the 1972 men's 400 individual medley.

"It's amazing to tie for gold. I never thought I'd win. She deserves it as much as me," said Oleksiak. "I'm only 16 so it's pretty insane to win a gold medal in your first Olympics."

Oleksiak has now collected four medals from Rio -- the most by a Canadian at a summer Games.

Manuel's first gold also comes at her first Olympics where she, as an African-American swimmer, also had a particular resonance.