The violence has disturbing echoes of the 1980s unrest
Union activists have shot and wounded two police officers during clashes in the French Pacific territory of New Caledonia, local officials say.
Four activists were injured and 13 detained in the clashes in Saint Louis, near the main island's capital Noumea.
The USTKE union represents indigenous Kanak workers. It has blocked roads and businesses with barricades of burning tyres during a week-long strike.
New Caledonia saw serious ethnic unrest during the 1980s.
France is sending extra gendarmes to New Caledonia to end the violence.
The latest trouble sprang from a dispute with the management of the local airline Aircal.
In June the USTKE leader Gerard Jodar was jailed for a year for obstructing an aircraft, after militant USTKE members invaded the Magenta airfield, French media report.
The French high commissioner in New Caledonia, Yves Dassonville, said "this is no longer trade unionism, it's pure violence, it's hooliganism".
Several businesses have been forced to shut down because of the protesters' action.
Under the 1998 Noumea Accord, New Caledonia received greater autonomy from France. It also created New Caledonian citizenship.
In 2006 the French parliament approved plans to restrict the voting rights of French citizens in the territory, meaning that Kanaks would get real power to run their own affairs.