The Rural Fire Service in Wairarapa says it is treating a large fire in a commercial pine forest southeast of Martinborough as suspicious.
It says the fire, which has been burning since Monday morning, is now contained but it could take days or weeks to properly put it out.
It has burnt through between 70 and 100 hectares of pine trees.
Wairarapa principal rural fire officer Phil Wishnowsky says it represents a significant loss of investment and the owners of the plantation are extremely upset.
The Fire Service says it was called to the scene off Pahaoa Road in Hinakura about 5.50am on Monday.
About 60 firefighters battled the blaze into Monday evening with the help of eight helicopters, six fire trucks and a command unit.
A team of rural fire officers from Wellington and Wairarapa and a command unit from Wellington were sent in on Tuesday.
