Police have confirmed that arson caused the fires at Whakapapa skifield on Mount Ruapehu skifield.
Two buildings at Whakapapa were destroyed and a third damaged in the fires early on Saturday. The damage bill is $5 million.
Police said on Monday the fire was lit in three separate places and that traces of an accelerant have been found.
The company that operates the skifields has expressed disbelief at the news.
Ruapehu Alpine Lifts general manager Dave Mazey says he cannot understand why anyone would do such a thing.
