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 a passenger aircraft that had lost radio contact, and had been 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.

The spokesman said the fighter emitted its sonic boom over the east of Paris.

The defence ministry said in a statement the Rafale had gone to the aid of an ERJ 145 passenger plane, a 50-seater made by Brazil's Embraer, flying from Brive in the southwest to Saint-Brieuc in the northwest.

"Despite an altitude of more than 10,000 metres, the atmospheric conditions meant the supersonic boom was strongly felt in the Paris metropolitan area," it said.

Radio contact was re-established with the passenger plane and it reached its destination safely as the Rafale stood down.

The same fighter jet had been called out earlier Wednesday to check a Falcon 50 plane that had lost radio contact which was also reestablished, it said.

The French air force said the jet was authorised to travel at supersonic speed
The French air force said the jet was authorised to travel at supersonic speed AFP / ALAIN JULIEN

France's DGAC civil aviation authority played down the seriousness of the incident, saying such events happen "regularly". In 2019, the French air force counted 450 "abnormal" aviation situations, 210 of which required intervention by fighter jets or helicopters.

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 at 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 satirical weekly 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.