A strange mist that appeared at Sir Peter Jackson's three-storey Wairarapa mansion has defied explanation.

A caretaker called firefighters to the director's Masterton estate, after a fire alarm was set off at about 6pm yesterday.

Masterton fire station officer Garry Nielsen said they found no sign of fire or smoke, but discovered an unknown mist that was contained to one room.

"We ventilated it and it didn't come back, so we checked everything out. It didn't appear to be a problem, so whatever caused it, it stopped happening,'' he told APNZ.


Mr Nielsen said he was not concerned that they could not identify the mist.

"We don't know what it was and that doesn't particularly concern us, because we occasionally get something that's unknown - electrical smells or something like that. That just seems to be just a blip.

"We've got thermal imaging cameras, we've got different things, so we just make sure there isn't a risk of fire, and that's our job done.''

Sir Peter and his wife Fran Walsh were not at home at the time.