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

Government-owned Solid Energy announced on Thursday it was placing itself in 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 4m metric tons of coal each year, about 70% 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 more than $300 a metric tonnes in 2011 to about $85 now.

This month it emerged the country’s last coal-fired power plants will be shut down as a result of cheaper renewables and falling demand.