Video: tennis players at the French Open shaken by Sonic boom

A tennis player at the French Open was visibly surprised by a sonic boom Wednesday just as he was about to serve a ball.

Before the cause of the loud blast was known, there was a brief moment of panic outside the Roland Garros grounds in western Paris when police officers gave instructions to cordon off the area with the possibility of evacuating people. Some security officers ran down Boulevard d’Auteuil, a long path that leads to one of the main entrance doors, shouting into walkie-talkie radios.

A few minutes later, the police revealed the cause of the noise: a fighter plane breaking the sound barrier.

“A very loud noise was heard in Paris and in the Paris region. There is no explosion, it is a fighter plane that has broken the sound barrier,” police wrote on Twitter. “Don’t block the help lines!”

A police officer on Boulevard d’Auteuil approached a security officer guarding the gates and told them it was a “false alert” before joining his colleagues on their patrol.

The French Air Force explained that the plane was authorized to break the sound barrier because it needed to check a small civilian plane that had lost contact with air traffic controllers.

But without warning, residents of Paris, along with fans and players within Roland Garros, expressed their fears of an explosion on social media. Roughly 45 minutes later, nearly 17,000 people had retweeted the reassuring news.

On the Suzanne Lenglen pitch, the second largest stadium at the French Open, Dominik Koepfer was interrupted mid-service by loud applause.

His shoulders slumped and he retreated from his serving action, then looked across the net at opponent Stan Wawrinka. The Swiss looked equally puzzled as he stood perfectly still before the game finally continued.

“It was a bit strange, we both stopped. We both looked at each other and we didn’t know what it was,” Koepfer said. “It was a strange feeling, for a point or two I thought about it.”

Wawrinka, the 2015 French Open champion, quickly sought to find out what happened.

“I was surprised, like everyone else. It was certainly a concern. I asked the referee to let me know what it was,” said the three-time Swiss Grand Slam champion. “Everyone had the answer pretty early, so everything was fine.”

Elina Svitolina was playing Renata Zarazua on the Philippe Chatrier court, the biggest stadium in the tournament, when she heard the noise.

“I was a little worried because I thought something bad had happened. I looked at the chair umpire, he was also a little surprised,” said third-seeded Svitolina after winning. “You never know these days what can happen, what is happening. It was very strange, very noisy, as if something big fell.”

Five years ago, when France was playing Germany in a soccer friendly at the Stade de France, two explosions started a wave of deadly terrorist attacks in Paris.

The first blast went almost unnoticed by players on the field that day, but the second caused French defender Patrice Evra to stop playing with the ball at these feet as he looked up trying to understand what he was hearing.