Prime Minister Manuel Valls is visiting the city today.

Elite police troops were being sent to the scene in the northern suburbs of the Mediterranean port city, the source said.

Caroline Pozmentier, deputy mayor of Marseille, suggested the incident was part of a problem of drug trafficking in the area.

A school had been evacuated, she said, adding: "This battle against drug trafficking is a long-term battle."

France has been on high alert for security incidents following the Islamist attacks in Paris last month that killed 17 people.

Last week, two soldiers protecting a Jewish organisation and radio station were wounded in a knife attack in the city of Nice.