A gunman claiming allegiance to the Islamic State group fired shots and took hostages at a supermarket in southwestern France on Friday, a local prosecutor said.

Security forces were responding to two separate incidents, one at a supermarket in the town of Trebes and the second, a 15-minute drive away, in the town of Carcassonne where a policeman was shot.

It was unclear if the two incidents were linked.

In Trebes, the man "entered the Super U supermarket at around 11.15 am and shots were heard," a security source told AFP on condition of anonymity.

The gunman claimed allegiance to the Islamic State group, the local prosecutor's office said.

Local authorities tweeted that the area was off-limits to the public.

If the link to Islamic State is confirmed, the attack would be the first major incident since the election of centrist President Emmanuel Macron in May last year.

The shootings come with France still on high alert after a string of jihadist attacks since 2015, starting in January that year with the assault on satirical magazine Charlie Hebdo that left 12 people dead.

France also suffered major attacks in Paris in November 2015 when IS jihadists killed 130 people at bars, restaurants, the Bataclan concert venue and the national stadium.

In July 2016, in another attack claimed by IS, a man drove a truck through revellers celebrating Bastille Day, killing 84 people. 

A state of emergency put in place just after the Paris attacks was finally lifted in October last year, but soldiers continue to patrol major tourist sites and transport hubs under an anti-terror mission.