A block of flats in Hokitika was extensively damaged by fire last night.
Fire crews from Hokitika, Ross and Greymouth took more than four hours to put the fire out.
Police said only one of the Fitzherbert St units was currently tenanted and they believed the occupant was out of town at the time.
One tenant in another building on the site was evacuated as a precaution.
Police said the block would need to be made safe before investigators could enter the scene and begin working out what caused the fire.
They would like to speak to anyone who was in the area around the time it broke out, shortly after midnight.