MELBOURNE, Jan 31 (Reuters) - New South Wales is set to finalise an order by mid-February that will require all mining firms in Australia's biggest coal exporting state to reserve as much as 10% of their output for domestic supply.

A Department of Planning and Environment spokesperson said the government would issue final directions after talks with miners.

"The draft revised directions allow suppliers the option to provide coal from their own production or to strike an agreement from another supplier to meet their obligations under the directions," the spokesperson said.