A teenager in New Caledonia has admitted causing the massive fire in an industrial zone of Noumea two weeks ago.
The 17-year-old had been detained with two younger teenagers a week after the blaze.
The suspect is free and will be tried in the youth court.
The fire engulfed the plastics and paper businesses Cellocal and Sofaplast, burning 100 tonnes of highly flammable material.
It took about 100 fire-fighters 40 hours to bring the fire under control.
The effort prevented the flames from spreading to an adjacent tyre business.
About 60 employees were affected by the fire at the businesses which belongs to the Lafleur group.