Members of New Caledonia's CSTNC union have clashed with police after the police lifted a union blockade outside the SLN mining company in Noumea.
The clash occurred after police intervened before dawn and as tension mounted again when more unionists arrived at the SLN.
Between 400 to 500 protesters were pushed back by police when they tried to march into the city centre.
In the early afternoon, the protesters were still on the main road into Noumea with about 100 members of the police force standing by.
As a result the main road is closed and traffic has been diverted through other routes.
The leader of CSTNC, Sylvain Nea, has warned of a sharp response to today's action by the police riot squad.
Mr Nea says there will be no more nickel leaving the plant next week and warns that SLN should prepare a shut-down of its furnaces in response to the police action.