Four people - two security guards and two migrants - were fatally shot on the Loon-Plage stretch of coastline near Dunkirk, unnamed security sources told outlets in France.
The gunman is alleged to have also confessed to an earlier shooting in the nearby town of Wormhout, according to AFP.
Local media said weapons were found in the suspect's car and Dunkirk's Mayor Patrice Vergriete said the motive behind the attacks "remain unknown".
BBC News has contacted local authorities for comment.
Vergriete described the incident as a "tragedy" and said "an individual coldly murdered several people" in the area.
Xavier Bertrand, head of the region's assembly, confirmed on X that five people had died in a "tragic event".
French media reported a large emergency services presence close to a migrant camp, though it is unclear if the shootings took place inside a settlement.
Loon-Plage is home to several temporary settlements housing migrants. It is near to Calais and the Strait of Dover, which is the narrowest part of the Channel.
Similar camps along France's northern coast have been used by people attempting to reach the UK via small boats, the report added.