Lizzy Hawker at the finishing line in Chamonix. Photo: Chiara Dendena

British athlete Lizzy Hawker’s win in one of Europe’s toughest mountain races was achieved on a revised route lengthened following the discovery of potential danger on part of the planned course.

The Ultra-Trail du Mont Blanc start was also delayed by five hours as an Alpine storm hit part of the course. A potential rockfall led to organisers introducing a diversion, stretching the race to 170km and making it the toughest since it was first run.

The North Face runner was first woman from a field of 86 to cross the line in Chamonix, and was placed 13th overall with a time of 25hrs 2mins, the second fastest ever on the UTMB by a woman, and a record-breaking fourth win – her previous victories coming in 2005, 2008 and last year.

A field of 2,370 runners started the course, which roughly follows the course of the Tour du Mont Blanc walking route through France, Switzerland and Italy.

Spaniards Kilian Jornet and Iker Karrera were first and second overall respectively, with Sébastian Chaigneau of France third. Despite variable conditions including rain, snow, and extreme high and low temperatures, it was the fastest course to date.

Hawker, who was almost three hours ahead of the next fastest woman Nere Martinez Urruzola, said: “With a race like The North Face Ultra-Trail du Mont-Blanc you have to run with courage and humility. It was something very special to share the trail with so many people with passion for mountains and trails.”

Jez Bragg: 'breathing was unsustainable'

Dorset-based Jez Bragg, winner of last year’s race, had to pull out of the race due to health reasons after a recent infection combined with the harsh weather. He said: “I am really disappointed. I was moving well and my legs felt really strong, but what I had to do in terms of breathing was unsustainable.

“Very soon after leaving Champex Lac it became so difficult to breathe, I made the decision to retire from the race.”

Electronic chips carried by the runners allowed 1,700 of the competitors to share their race progress in real time on personal Facebook and Twitter pages using the LiveTrail application.

From start to finish line, live updates were posted from the course as checkpoints were passed enabling followers globally to track their runner. About 4,800 automatic Tweets and 24,000 automatic Facebook posts were recorded by LiveTrail on runners’ profiles and walls.