The incident on the day after Christmas prompted the evacuation of all staff from the seven-billion US dollar plant in the territory's north and led to a temporary stop to production.
There are no reports of any injuries.
About 500 tonnes of liquid nickel was spilled from one of the furnaces for reasons yet to be determined.
According to the territory's public broadcaster, the first results of a probe of the incident are due by tomorrow.
The plant, which was officially opened by the French president Francois Hollande last month, experienced a blast just before Christmas, briefly affecting production.
The Koniambo plant is widely seen as the key industrial site to advance the economy of the mainly Kanak northern province.
Radio New Zealand