New Caledonia's Vale-Inco nickel company says there has been a spill of 670,000 litres of a solution containing acid.
The company says nobody was injured and the spill was contained by the tailing dams.
The plant, which cost about four billion US dollars to build, is still in its testing phase although production was due to start last year.
Last April, the company suffered a major setback when thousands of litres of acid was spilt into the lagoon which is a World Heritage site.
