Two Australian rowing coaches have been robbed at knifepoint near Rio's famous Ipanema Beach in a troubled start to the Olympic Games, which also featured a stray bullet being shot into a media room and an explosion occurring near the finishing line of the men's cycling road race on the opening day of competition.

The two male Australian officials were wearing their team uniforms and were walking the short distance back to their hotel, after attending the Australian team's informal opening ceremony on Ipanema Beach, when they were confronted by two male teenagers about 8.30pm on Friday, local time, Australian Olympic Committee spokesman Mike Tancred said.

One of the teenagers pulled out a knife and threatened the pair, while the other teen grabbed one of the coaches by the throat and demanded he hand over his money, Mr Tancred said.

"One coach was robbed of his wallet which contained a credit card, and he also lost his team blazer which he was carrying over his arm at the time. They both lost their mobile phones," Mr Tancred said.