Canada's Magdeleine Vallieres won the women's road race on a long, gruelling course over the hills of Kigali at the cycling world championships on Saturday.

The 24-year-old broke late on the 167km run over 11 circuits of the Rwandan capital to win ahead of New Zealand's Niamh Fisher-Black and Spain's Mavi Garcia in third.

Starting the day ranked 131st in the world, Vallieres got away from the other medallists on the last of the 15.2km laps of the circuit on a testing cobbled climb and crossed the summit finish alone completely exhausted.

"I can hardly believe it," said Vallieres after by far her biggest career win. "I just got in the right break," she explained after finishing 23 seconds clear.

"I prepared well, I knew I was on good form, so I tried. I told myself I didn't want to have any regrets. And I don't," said Vallieres.

"It's great to win here, and with the worlds next year in Montreal, it's been perfect. It was my dream to win it, and now it's come true - it's crazy."

Tour de France champion Pauline Ferrand-Prevot started as favourite but was heavily tracked by her rivals as they mistakenly allowed a small group to get over a minute ahead.

Ferrand-Prevot eventually trailed home alongside American Chloe Dygert almost two minutes down.

"This kind of thing often happens in a world championships. I'm more disappointed for the team than myself," said Ferrand-Prevot, the Frenchwoman who won the Olympic mountain bike title in Paris.

Dutch rider Anna van der Breggen dropped back with 30km to go while last week's time-trial champion Marlen Reusser made a brave but doomed solo effort to counter-attack.

These are the first cycling worlds to be held in Africa.

The winners are awarded a rainbow jersey that they wear for the year, a much coveted prize in a race where riders represent their nation rather than a professional team.

The men's race is on Sunday and is extremely long at 267.5km. It includes 33 climbs over 15 loops and one longer, even harder circuit with an extra cobbled climb.

Favourite Tadej Pogacar said the humidity and altitude were potentially decisive factors.

"We're quite high here and you can feel it, not so much walking around, but on the bike. Also, the air quality here in the city is not the best," he said.