Solid Energy is taking urgent action to deal with what it calls an unacceptable level of accidents at its Stockton open cast coal mine in Buller.
The company says there have been some injuries during various accidents on the mine roads in the past nine months.
It will spend $50 million to upgrade infrastructure, including roads, in the next 18 months.
Overtaking on the mine roads has been banned.
Solid Energy says staff numbers at Stockton have doubled in two years and this is contributing to increasing incidents.
The main union at the Stockton coal mine in says a lack of training for workers has contributed to the sharp rise in workplace accidents.
Engineering, Printing and Manufacturing Union spokesperson Dave Reece says there have been 120 incidents in the past year, many on the mine roads - with about a dozen resulting in accidents.
Mr Reece says Solid Energy has not properly dealt with the growth of the mine or the doubling of staff numbers, and believes its plans for improvements are overdue.
