The Tour's 13th stage got under way with tightened security after riders had observed a minute's silence in tribute to the scores of victims of the Bastille Day attack in the south of France.

A gunman at the wheel of a heavy truck ploughed into a crowd celebrating Bastille Day in Nice late on Thursday, killing at least 84 people and injuring scores more in what President Francois Hollande called a terrorist act.

Elvin is in Europe finalising her Games preparation and said the constant threat of terrorism has become "a way of life".

"Everyone is concerned, it definitely hit close to home this year with the Belgium airport bombings, all cyclists use that airport probably more than any other airport," Elvin said.

"Because of big events like the Tour de France it becomes a target, so we're all trying to be vigilant, but in some ways you really can't do anything except to just keep an eye out.

"You still have to live your life and race the race and enjoy it. We're all concerned but we're going to keep on keeping on and enjoy our awesome sport."

Retired Canberra world champion Michael Rogers has previously voiced his concerns about crowd safety and the threat of terrorism at cycling's showpiece event.

Organisers debated on Friday whether to continue the race or cancel the following stage after the events in Nice.

"We had a crisis meeting with the prefect of the Ardeche department and the gendarmerie. The stage is on," said race director Christian Prudhomme.

"We want this day to be a day of dignity as a tribute to the victims. We asked ourselves [whether the stage should be cancelled] but we think, after agreeing with authorities, that the race must continue."

Elvin's selection for the Rio Games was announced this week, and while the global threat of terrorism is increasingly present, she said she was confident in the security measures in place.

"I know that the Olympic committee is doing everything they can to ensure the safety of athletes, and then on top of that we have the Australian Olympic Committee as well. I'm not too stressed going over there but I'm definitely going to be more cautious than say the London Olympics."

And while she admits the hysterical fans blocking roads and impacting on the Tour is generally limited to that race, the events of Thursday where race leader Chris Froome crashed out are disturbing.

"It does scare me, I watch the Tour de France as much as I can and cringe when I see spectators get so close, and then yesterday when the motorbike had nowhere to go, it was completely not their fault, and it effected the race hugely.

"I'm assuming that most of it will actually be fenced off, so I think we won't see as much fans obstructing the race as we have in the Tour, but you never know."

Rogers said last year the vast distances covered by cyclists, most of which with no barriers between spectators and riders, posed difficulties for authorities.

"You could only imagine the expense for the organisers to barrier the whole circuit for hundreds of kilometres. I don't think that's a feasible thing to do," he said.

"It's been in the back of my mind, events such as the Tour, a big international event where the whole world is watching.

"A lot of riders do think about it because we pass a lot of people by the side of the road and it's quite easy for a potential attack.

"I hope the authorities are doing work in the background making sure the course is clear, but it's certainly becoming an issue," he said.

Tour de France riders including Froome sent messages of support to the victims of the terrorist attack.

The defending champion posted a picture of the blue, white and red French flag on Twitter on Friday and wrote: "Thoughts are with those affected by the horrific terror attack in Nice."

French climber Romain Bardet also expressed sadness over the attack.

"Being French, gathering, celebrating, loving each other," he posted on social media. "And never giving up. I'm thinking about Nice."

– with AAP.