With just one week to go before the opening ceremonies for the Sochi Games, security experts say the Olympic venues are now among the most protected in the world. But questions remain over the vulnerability of the rest of Black Sea resort town.

Bud Mercer, the former head of security for the 2010 Vancouver Olympics, said it's not the venues that are of concern, but the other parts of Sochi located away from Olympic sites.

"I have little doubt that the venues, the villages, the (Olympic) routes… there will be a very high level of security," he told CTV's Canada AM. "But Sochi is a very large city along the Black Sea… It's also a resort town with a high level of visitors and guests. That's the challenge they'll have."

Mercer said that there's still a "long road ahead" for the Sochi organizers, as they fine-tune their security plans just as athletes, dignitaries and spectators begin to arrive.

"Right now, they're entering the busiest time," he said. "They're getting ready for the opening ceremonies, which of course puts a lot of the world's athletes in one facility, plus a high number of internationally protected people and dignitaries from other countries.

"So they've got their hands full."

Members of Canada's Olympic team are beginning to arrive in Sochi, with figure skater Patrick Chan and snowboarder Mark McMorris set to arrive Friday, CTV's Peter Akman said Friday from the Sochi airport.

Akman said he's already seen members of the U.S. Olympic team arrive.

"They were all wearing their full 'U.S.A' uniforms," he said. "Some of the concerns of them wearing them outside the 'safe zones,' but some of them say they'll wear them regardless of the warnings."

On Sunday, International Olympic Committee President Thomas Bach is slated to meet with members of his cabinet to review the final security plans for the Games.

Russia has promised to deliver the "safest Olympics in history," and has assigned about 100,000 police officers, security agents and members of the army to help secure the Games. As well, a variety of defence tools have arrived in Sochi, including air defence missiles, drones, and high-speed patrol boats.

But despite the sizable security presence, fears of a terror attack remain. The Canadian government issued an updated travel advisory on Thursday, warning people travelling to Sochi to avoid taking public transit.

Fuelling the fears are two December suicide bombings in the city of Volgograd, located about 650 kilometres east of Sochi. A militant group from Dagestan claimed responsibility for the bombings, which killed 34 people, and threatened to strike the Olympic Games.

Dagestan is considered one of the centres of the Islamic rebellion that's gripped the Caucasus region of Russia.

On Thursday, Russian security officials identified two brothers suspected of being responsible for the Volgograd attacks and announced the arrest of two men suspected of helping the brothers.

Leaflets have also been recently distributed in Sochi, warning of three potential female "black widow" bombers who may be in town. Police identified one of the suspects as Ruzanna Ibragimova, a 22-year-old widow of an Islamic militant.

Sochi residents have also been subjected to a series of blanket police checks, with officers going door-to-door in recent months in an effort to hunt out any terrorist activity.

But Alexander Popkov, a local lawyer, told The Associated Press that the checks were mostly superficial.

"I don't think they would have uncovered a terrorist cell," he said.

With files from The Associated Press