Fire safety officers and police were treating the latest fire as "very suspicious", Oamaru fire chief Steve Couper said yesterday when contacted.
The fact that it was again at night and opposite the Tenby St house gutted by fire on September 8 made it suspicious.
The September 8 fire had been confirmed as arson, but yesterday's blaze was still under investigation.
The Palmerston, Hampden and Oamaru fire brigades were called out about 1am yesterday.
They were assisted by units and tankers from Weston and Kakanui.
At its peak, about 25 firefighters were fighting the blaze and they were at the house until about 6am.
Mr Couper said that when he arrived, the two-storey house, built into the hill with a garage underneath, was well alight and already partially destroyed.
Tankers had to travel to Hampden to get more water to fight the fire.
There were fears embers could be blown by a strong southwest wind to two neighbouring properties, both of which were unoccupied at the time, and the firefighters' priority was to prevent it spreading.
"We have some concerns [about the fire], so police and fire safety are investigating," Mr Couper said.
About 9.15pm on September 8, the Palmerston, Moeraki and Hampden brigades were called to a similar fire that gutted an unoccupied, single-storey holiday home. Police and fire safety officers investigated that fire, which was suspected to have started outside the two-bedroom, wooden crib.
The fire spread quickly through the interior of the house, except for one room behind a closed door.
Detective Warren Duncan, of Oamaru, said yesterday's fire was being treated as suspicious.
The previous week's fire was being treated as arson, he said.
He urged people who lived in the area to be extra vigilant in monitoring suspicious activity and suggested those with unattended properties check them for any sign of irregularity.
A concerned Moeraki resident, who declined to be named, said the settlement was full of such properties and he was worried about the fires.
"Very few people live around here now.
"Half the houses in Moeraki are unoccupied."
Another resident described it as "a bit weird and odd. People are wondering what's going on."
Some residents contacted did not want to comment, for fear of being targeted.
