The French city of Marseille was thrown into panic today by reports of two 'powerful detonations' amid fears of a terror attack.

But it now appears to have been a false alarm, possibly caused by a sonic boom from a fighter jet passing overhead.

Social media went into meltdown when a Marseille resident claimed there had been at least two 'powerful detonations' in the city in southern France.

Others reported hearing the blasts and said the windows of their houses shook although some on Twitter suggested it may just have been a sonic boom from a fighter jet flying overhead.

The Old Port in Marseille, scene of today's mystery 'explosions', thought to be a sonic boom

Russia Today said there had also been reports of sirens in the city.

But the local newspaper, La Provence, tweeted: 'Many of you report an explosion noise heard at #Marseille. But firefighters and police report no intervention.'

A French fire service spokesman in Marseille said: 'We have also heard a blast but its origin is, for now, mysterious.'

Tomas Thurogood-Hyde tweeted: 'Worrying reports about explosions in #Marseille. We will all hope this is not terrorism; #France has suffered too much already.'

France remains on high terror alert following the attacks in Paris and last year's lorry attack in Nice.

The noise may have come from a sonic boom caused by a supersonic fighter jet, such as a French Dassault Mirage (pictured) flying over Marseille STOCK PHOTO

Elections in the spring will see the rise to power of a new President, possibly the Far-Right Marine Le Pen, who has promised to crack down on migrants and Islamist extremists.

Sonic booms are a loud banging noise caused by an object flying through the air faster than the speed of sound.

They were commonly heard when Concorde was flying but passenger jets are not fast enough to cause the noise, which would more likely have come from a supersonic fighter jet, possibly one of the French air force's fleet of Mirages.