No one was in a South Island house engulfed by fire late last night.

Southern Fire Communications shift leader Rewi Grace said firefighters confirmed after midnight that no one was in house at Runanga, near Greymouth.

However, the fire, which began about 11pm, is being treated as suspicious and police and fire investigators will arrive later today, Mr Grace said.

One fire crew remains at the scene to dampen down hot spots, and a guard will remain on site overnight, he said.