The extreme form of triathlon in the American state saw athletes begin with a 2.4-mile ocean swim in Kailua Bay.

This was followed by a 112-mile bicycle ride along the Queen Ka'ahumanu Highway from Kailua-Kona to Hawi, before a marathon run.

Great Britain's Lucy Charles and Lauren Brandon of the United States dominated the swim and enjoyed a three-minute lead as they left the water.

Charles retained the lead as she approached the end of the cycle, where Ryf left the chasing pack and mounted her assault.

Thanks to the fastest run on the day, Ryf was able to put a nine-minute gap between her and the rest of the field and went over the line first in 8 hours 50min 47sec. 

"It was the hardest I had to ever fight for the win," said Ryf.

"I'm so happy to turn it around today."

Charles held on for second in 8:59:38 to mark an impressive debut while Australia's Sarah Crowley completed the top three in 9:01:38.

In the men's race, Patrick Lange improved on his bronze medal from last year to take gold.

The German posted an incredible time of 8:01:40 to break Australian Craig Alexander's 2011 course record of 8:03:56 in the process.

Australian rookie Josh Amberger started strongly to put a sizeable gap between him and the rest of the field in the swim.

Amberger maintained his lead until the climb to Hawi began but surrendered it to Canada's Lionel Sanders.

Australia's Cameron Wurf, in his sixth ironman race of 2017, was first off the bike with a new bike course record of 4:12:54 but Sanders entered the run just a minute behind.

By the half-marathon point Lange had moved into third and and was six minutes behind Sanders, who had now taken the lead.

Lange continued to chew into Sanders' lead, and by 23 miles, had overtaken the Canadian and went on to cross the line first.

"I always, always, since I was a child, dreamed of this," said the German.

A fading Sanders managed to hold off David McNamee for second in 8:04:07, while the Briton took third in 8:07:11