Bullets, a controlled explosion and muggings marred the start of the 2016 Olympic Games and raised serious security concerns in Rio de Janeiro - all before day three.

Day one kicked off with a loud boom in the Brazilian capital, rattling athletes and spectators near the finish line of the men's cycling road race.

Then at lunch-time a stray bullet pierced the media tent at the equestrian centre, narrowly missing a Kiwi official.

Despite fears of a bomb, Olympic officials revealed the morning's loud boom was in fact an unattended bag that was blown up as a safety precaution.


Organising committee spokesman Mario Andrada said the decision was in reaction to "global worry". "In a way it's good that they opt for the safe side."

Meanwhile, the origin of the stray bullet in the media tent remained unclear.

Andrada said no one had been hurt in the incident and authorities would investigate.

The New Zealand Olympic Committee said it appeared the bullet had been fired "unintentionally".

The scares followed a man being shot dead in a suspected armed robbery near Maracana Stadium hours after the opening ceremony and an attempted mugging the day before which ended with a Russian vice-consul fatally shooting a man.

Drama continued in the sporting arena, with a French gymnast seriously breaking his leg in a vault landing and rowers competing water more suited to whitewater rafting. Conditions were so bad Rowing NZ laid a complaint that the racing was allowed to continue on day one of the heats.

NZ chef de mission and former Olympic single sculls gold medallist Rob Waddell said the rowers' perseverance was a testament to their skill.

Six of the seven rowing crews won their heats.

The New Zealand women's sevens team also performed strongly, beating Kenya 52-0 and Spain 31-5.