New Zealand's largest coal miner has been forced into a managed bankruptcy due to a steep fall in coal prices.

Government-owned Solid Energy announced Thursday it was placing itself into voluntary administration, a process it hopes will allow it to keep trading as it tries to sell its assets. Whether any of its coal operations remain viable will be up to any potential buyers to decide.

The company employs 540 staff directly and another 200 contractors. It has been mining about 4 million metric tons of coal each year, about 70 percent of which is used for making steel.

The company said its large debt was exacerbated by a drop in the price for hard coking coal from over $300 per metric ton in 2011 to about $85 now.