Hall, 35, was involved in a fatal collision with a car about 6.22am near the intersection of the Monaro Highway and Williamsdale Road.

He was taking part in the Indian Pacific Wheel Race, a solo, unsupported ride covering almost 5500 kilometres, that crosses the Nullarbor Plain then winds through Adelaide, Melbourne and then Sydney.

He had briefly led the race in the Snowy Mountains when he overtook Belgium's Kristof Allegaert, who was having a meal at the time.

But when Hall took a rest break, Allegaert grabbed back the lead and had been expected to win the race at the Sydney Opera House on Friday afternoon.

At lunchtime on Friday, the organisers put out a statement saying the race had been called off.

"The Indian Pacific Wheel Race has been cancelled with immediate effect in light of this morning's tragic incident," the statement said.

"Every effort is being made to personally get in contact with riders that remain on the road to inform them of the situation.

"The tracking devices will remain open in the interests of safety and the event is continuing to work with the relevant authorities.

"This is a difficult time for everyone involved, along with their families, and their wellbeing is our primary concern."

Hall was one of 70 riders who set off on March 18.

He has won one of the world's longest mountain bike races, the 4400-kilometre Tour Divide from Canada to Mexico across the Rocky Mountains, and the world's longest road bike race, the 29,000-kilometre World Cycle Race.

When Hall's dot on the official race tracker stopped at 6.52am, he had ridden 5024 kilometres in just over 12 days - averaging more than 400 kilometres a day.

Before confirmation of his identity, the race organisers issued a statement saying they were working with local authorities after a collision between a vehicle and a cyclist at Royalla.

"We will co-operate fully with official investigations and we intend to undertake a detailed investigation of our own," the statement said.

A personable British design engineer with a sense of humour, Hall had earlier reported having vision problems riding at night.

In a Curve Cycling video on day 12 of the race, he noted that the previous night "all the glare of the light hitting the signage and the road furniture just swirls around and blurs about.

"I've been thinking that I can't stay awake because I'm just really tired but it's just the fact I can't see in the dark properly ... I was kind of like all over the road like this - can't see - for a while after it got dark."

His last tweet early on Thursday - just after midnight - was about realising that he might need glasses.

Four days earlier, Hall had tweeted about his concern with cars passing intimidatingly close to his bike.

Three days before that, Hall tweeted his sympathies to victims of the terrorist attack in London.

Hall had previously talked about how dangerous he found Australian drivers in a world circumnavigation ride in 2013.

"Cars will go past you at 110, 120 kilometres an hour, leaving you about a foot gap, and there's a whole other lane free," he said. "It's crazy ... It's been some of the worst driving with regards to safety that I've seen."

Fans of a race that had become an epic endurance event over the first 12 days - so-called "dot watchers" given that the website tracker was the best way to follow cyclists over such long distances - reacted with shock even before Hall had been confirmed as the rider who had been killed.

Todd Niehaus commented on Facebook: "I'm at the store with my daughter. Just read the press release. We are both crying."

Jon Thonton wrote "This is just the most horrible news."

And Kaity Bradey said: "Devastating, absolutely devastating ... it just makes me feel ill."

Up to the final day, the IndyPac had been an enthralling race full of inspirational stories.

The three leaders - Allegaert, Hall and Sarah Hammond - had been greeted warmly as they raced across the country in what had been dubbed "the Hunger Games on wheels".

They were riding long distances every day and grabbing short bursts of sleep, often camping beside the road, before getting back into the race.

The field included Paul Ardill, 74, who was partly racing to take his mind off the sudden death of his triathlete daughter Cheri Lutz last year, and long-time cycling journalist Rupert Guinness, 55, who was inspired by the feats of the pioneer outback cyclists.

Being an unsupported race, the riders carried what food, water and repair supplies they could, then bought supplies at service stations, supermarkets, cafes and bike shops along the way.

It's an event that attracted hardy souls who were prepared to overcome the inevitable setbacks on such long, unsupported events.

British-German cyclist Juliana Buhring rode 1100 kilometres before being forced to withdraw due to an allergic reaction to painkillers.

She hitched a ride back to Perth on a road train, received medical treatment and then, when she was well again, started the race again from Fremantle.

But on Monday, Eoin Marshall was forced to withdraw after being injured in a collision with a vehicle on the outskirts of Tarlee in South Australia.

The driver was charged with driving without due care.

The course of the Indian Pacific Wheel Race from Fremantle to Sydney. Photo: IPWR

???With Steven Trask