The bus was making its way from the Games basketball venue to the main Olympic park when, according to passengers, two shots were heard hitting the vehicle. Windows shattered and flying glass left two people with minor lacerations.
"We were shot at. I mean we could hear the report of the gun," said Sherryl "Lee" Michaelson, a retired U.S. air force captain who is working for a basketball publication in Rio.
A spokesman for the Rio organising committee, Mario Andrada, said forensic investigators were trying to determine if the projectile was a bullet or a rock.
"We haven't yet been able to confirm what kind of projectile hit the bus," he said, adding that the incident occurred in the Curicaca neighbourhood, just a few kilometres (miles) north of the Olympic Park. "We don't want to speculate."
A Reuters photograph taken in the first moments of the incident showed a small hole, about the width of a finger, in one of the windows.
Violent street crime in Rio has left its mark on South America's first Olympic Games. On Saturday, a bullet hit the equestrian centre, missing journalists there by just a few feet. That bullet was suspected to have been fired by a gang member trying to shoot down a police blimp or drone, officials said.
