RIO DE JANEIRO - Two gold medals were awarded in the women's 100m freestyle on Thursday but they did not go to the Campbell sisters.

Canada's Penny Oleksiak, 16, and American Simone Manuel, 20, both finished the blue riband sprint in an Olympic-record 52.70 seconds.

"I saw Simone's name and thought, 'OK, I came second', and then I saw that it said Olympic record beside both names," said Oleksiak. "It's crazy. No one ties at the Olympics really, but it was great to tie with her."

Sweden's Sarah Sjostrom claimed bronze (52.99sec).

"It's the most exciting finish I've ever had," said the 22-year-old, who also has a gold (100m butterfly) and silver (200m free) from these Games. "I wish I could have watched from the stands."

Reigning world champion Bronte Campbell, 22, finished fourth in 53.04sec. Older sister Cate, 24, was sixth in 53.24sec.

The Campbells were aiming to become the first Olympic gold and silver medal-winning siblings of an individual swimming event.

Instead, Oleksiak and Manuel made history, becoming just the second pair of women to share 100m free gold at the Olympics.

Americans Nancy Hogshead and Carrie Steinseifer both clocked 55.92sec to stand together at the top step of the podium during the 1984 Los Angeles Games.

The last dead-heat for Olympic gold in swimming was at the 2000 Sydney Games when Americans Gary Hall Jr and Anthony Ervin both completed the 50m free in 21.98sec.

"My first gold medal at my first Olympics is kind of a surprise to me," said Manuel. "I never thought I would be in this position."

Cate, the world record holder and 2013 world champion, was the favourite after setting an Olympic record time of 52.71sec in the semi-finals on Wednesday.

Defending champion Ranomi Kromowidjojo of the Netherlands was fifth (53.08sec).

The Campbell sisters have already made their mark in Rio though. Together, they helped Australia win the 4x100m freestyle gold in a world record time of 3min 30.65sec last Saturday.