Authorities weren't certain of what the hostage taker was demanding. No injuries were reported.
The youth seized the hostages at 4:20 p.m. (1420 GMT) in the town of Blagnac, near Toulouse airport, according to a national police spokeswoman.
The suspect was not known to police, the spokeswoman said, declining to divulge details of his identity while the standoff was still underway.
The teen later released all four hostages but remained inside the store, surrounded by police, another police official said.
Local state television France 3 reported that the hostage-taker fired three shots in the air, is wearing a helmet fitted with a camera and demanded to speak with a negotiator.
Police locked down the neighborhood, evacuating some buildings and ordering other residents to stay inside, according to neighbor Robert Texier. A police helicopter circled overhead.
The police spokeswoman and a security official said it was too early to rule out terrorism without knowing the hostage-taker's demands. Both officials spoke on condition of anonymity because they weren't authorized to be publicly named. The national terrorism prosecutor's office said it is following the situation.
"It's worrying. It all happened so quickly," said Texier, who expressed surprise at the incident in what he described as a quiet neighborhood on the banks of the Garonne River. He said the convenience store has been run for decades by a woman and her daughter who live in the adjacent building.
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