A thunderous noise that panicked residents of Paris on Wednesday was caused by the sonic boom of a fighter jet breaking the sound barrier, police in the French capital said.
The military said the jet was scrambled to go to the aid of another aircraft that had lost radio contact, and was authorised to travel at supersonic speed.
"A very loud noise was heard in Paris and in the Paris region. It was not an explosion, it was a fighter jet crossing the sound barrier," Paris police said on Twitter, urging people to stop calling emergency phone lines.
The noise, which was heard all over the city and neighbouring suburbs and shook windows, rattled Parisians already on edge after a knife attack outside the former offices of satirical weekly Charlie Hebdo last week that the government has called an act of terror.
"A Rafale, carrying out an intervention to assist an aircraft that had lost contact, was authorised to break the sound barrier to reach the aircraft in difficulty," a French air force spokesman told AFP.
No detail was given on the type of aircraft or the nature of its difficulty. The spokesman said the fighter emitted its sonic boom over the east of Paris.
France's DGAC civil aviation authority played down the seriousness of the incident, saying that a plane made by Brazil's Embraer had suffered "a loss of radio frequency" while flying over the west of France but that contact was re-established.
It explained such situations take place "regularly," In 2019, the French air force counted 450 abnormal aviation situations, 210 of which needed intervention by fighter jets or helicopters.
'You never know these days'
Wednesday's incident led to confusion, with people taking to social media to ask about a noise that many noted came without any apparent smoke or other traces of damage.
It was clearly heard during the French Open tennis tournament at Roland Garros, where star player Stan Wawrinka of Switzerland and his German opponent Dominik Koepfer paused in astonishment and apparent worry as the noise echoed around the stadium.
"Yeah, I heard it. I was a bit worried because I thought something bad happened," said Ukrainian tennis star Elina Svitolina after defeating Mexico's Renata Zarazua on the tournament's showpiece Court Philippe Chatrier.
"I looked at the chair umpire. He was a little bit shocked as well because you never know these days what can happen, what's going on," she said. "It was very strange, very loud, like something big dropped."
Last Friday, two people were wounded in an attack by a man wielding a meat cleaver outside the former offices of Charlie Hebdo in Paris.
The assault came three weeks into the trial of suspected accomplices in the January 2015 attacks on Charlie Hebdo and a Jewish supermarket.
Seventeen people were killed in the three-day spree of violence in 2015, including Charlie Hebdo staff and police officers.
The bloodshed heralded a wave of Islamist violence in France that has left 258 people dead. The nation remains on high terror alert.