French dock workers have stormed the port city of Le Havre and thrown smoke bombs into fountains, the Associated Press has reported.
The trouble comes amid widespread strike action over the country's controversial reforms to labour laws.
The unions are involved in a stand-off with the government over reforms which will make it easier for firms to hire and fire employees.
What's the optimum driving speed? Can you rely on jerry cans? Plus real-time information on how low fuel has got at French petrol stations.
Dozens of flights have been cancelled as air traffic controllers join the strike action in France.
The UK government warns people travelling to France that strikers blockading oil refineries have caused some stations to be without petrol.