The 100km Oxfam Trailwalker has been cancelled because of safety fears as protests continue to grip the city, the organisers have said. Participants can defer or refund their spots.

Concerns had been raised about the safety of the 5,000 runners and their support teams, who travel back and forth to the trails over the weekend, as the public transport system is crippled by protests.

Hong Kong’s oldest ultramarathon was supposed to start on Friday. Winners take around 12 hours, and the last cut off is 48 hours. It starts in Sai Kung and finishes near Tuen Mun, taking participants over the mountains of the New Territories. Almost 5,000 runners compete in teams of four, whose friends and family meet them at points of the course for moral support and to bring supplies.

Anti-government protests have caused the cancellation or postponement of a number of sporting events, including the Prudential Hong Kong Open tennis tournament, the 2020 Hong Kong Formula E-Prix, the The Hong Kong ASTC Sprint Triathlon Asian Cup, the Asian Aquathlon Championships, the Cross Harbour Swim, the Hammer Cyclothon and the Hong Kong Squash Open, and today, the Happy Valley horse races.

“The safety of our participants and volunteers is of utmost importance to us,” the organisers said. “In light of recent developments, transportation issues, in order to ensure the safety of over 10,000 participants, support teams and volunteers, and after much deliberation, we have made the extremely difficult decision of cancelling this year’s Oxfam Trailwalker.”

The organisers have promised places for those who wish to defer to next year, and refunds for those who do not. Those who have not picked up their race packs, with souvenirs inside, still can. And there will be refunds for shuttle bus tickets.

Hong Kong has been gripped by protests since June. What started as opposition to an extradition bill has grown into a wider and increasingly violent anti-government movement. While much of the protest action has taken place over weekends, the activists have sporadically sought to shut down the city's transport network during the working week too.

The organisers decision came after a morning of havoc, with traffic jams and delays across Hong Kong, including entire MTR lines closed.

On Tuesday, Oxfam Trailwalker said their decision would be made and announced by noon on Wednesday.

The 2018 Oxfam Trailwalker UK event was cancelled due to extreme heat.