The blaze, which began six days ago near the city of Nelson, is now threatening the town of Wakefield.
A state of emergency has been declared and about 3,000 people have fled their homes in the district of Tasman.
Strong winds were expected, and officials warned that Sunday could be a "critical danger point" for the fire.
Prime Minister Jacinda Ardern said she hoped "the weather plays ball".
The blaze is thought to be the worst forest fire in New Zealand since 1955.