Rio de Janeiro's Olympic security operation is under scrutiny today after it was revealed several unauthorised drones were flying above Maracana stadium during last night's opening ceremony.

At least three drones are believed to have hovered over the packed stadium, where 60,000 people, 27 heads of state and Olympic athletes had gathered to watch the Rio Games officially open.

Rio de Janeiro's Olympic security operation is under scrutiny today after it was revealed several unauthorised drones were flying above Maracana stadium during last night's opening ceremony

At least three drones are believed to have hovered over the packed stadium, where 60,000 people, 27 heads of state and Olympic athletes had gathered to watch the Rio Games officially open

Security sources told of 'moments of tension' after the drones were spotted as officials decided what action to take, while even Brazil's interim president Michel Temer is believed to have been made aware of the situation.

The scare is an embarrassment to Rio 2016 organisers who launched a massive security operation for the ceremony, with thousands of police and soldiers, a restricted zone around the venue and metal detectors and x-ray screening.

President Temer's security guards were also seen looking constantly to the skies as the show went on, appearing 'nervous' according to some spectators.

At around the same time, French president Francois Hollande, whose country has suffered several recent terror attacks, left the stadium accompanied by security personnel, although the reason is not known.

Team USA is seen at the opening ceremony held in Rio de Janeiro on Friday. Swimmer Michael Phelps served as flagbearer for the team

Around 10pm, at least three helicopters were sent above the stadium with orders to find the drones and destroy them, according to reports.

While the public watching the spectacle had no idea of the crisis, the sound of the low-flying helicopters could be heard above the ceremony proceedings.

In the roads surronding the Maracana arena, soldiers from the Nacional Security Force were seen pointing their guns to the skies in search of the unmanned aircraft, which have been banned from Rio for the duration of the Games.