Ledecky smashes 800m record to claim freestyle treble

Katie Ledecky reacts after winning and setting a new world record. (Reuters)

Katie Ledecky of the United States destroyed the field in the 800 meters freestyle on Friday, breaking her own world record to complete a rare Olympic swimming treble.

Ledecky led from the start and inexorably stretched out the gap over her opponents to finish in eight minutes, 4.79 seconds, beating her previous mark of 8:06.68 set in Austin, Texas in January.

Britain's Jazz Carlin won her second silver medal in 8:16.17, and Boglarka Kapas of Hungary took the bronze.

Ledecky, defending Olympic champion at the distance, added to her golds earlier in the week in the 200 and 400 freestyle and the 4x200 freestyle relay, plus a silver in the 4x100 relay.

The only previous woman to win the 200, 400 and 800 freestyle at the same Games was American Debbie Meyer in 1968.

"I've hit all my goals this past week... I just wanted to lay it all out there," Ledecky said after her final race in Rio.

"This was my last swim and the Olympics are the pinnacle of our sport.

"I have to wait another four years to have this moment and I just wanted to enjoy it all and put my very best swim out there."

Ledecky sliced 1.89 seconds off her own record in the longest event of the women's swimming program.

It was the seventh world swimming record of the Rio Games, and the second by Ledecky, who achieved a similar feat in winning the 400 freestyle.

Since winning the 800 in London four years ago, she has been invincible, and anything but a victory for the 19-year-old would have been one of the biggest shocks of the Games.

Carlin and Kapas fought a dogged struggle for second, with Spain's Mireia Belmonte Garcia challenging them for much of the way.