The cause of the Boxing Day blaze that consumed the Reed St house remained unclear yesterday, but Otago residents have rallied around the homeless family.
Sergeant Tony Woodbridge, of Oamaru, said investigating officers were yet to determine the exact cause of the blaze.
But they were treating it as suspicious and interviews with witnesses and those involved were continuing, he said.
"When I say `suspicious' there was no obvious cause, natural cause, for the fire to have started," he said.
"It is going to be a while before we can work out the exact cause."
Single mother-of-three Helena Nelson said she had been away from the house for just 20 minutes with her two young girls, before she returned to see it engulfed in flames.
Her 17-year-old son, Jackson, was napping at home and suffered burns to his face and arm.
A man living across the road said Jackson, who remains in Dunedin Hospital, was helped by a woman who "seemed to know what she was doing".
The woman reportedly sat Jackson down in a deck chair, hosed him off, then left the scene without speaking to police.
Sgt Woodbridge said police were eager to catch up with the mystery woman.
"We would love to hear from her and anyone else that was there early on."
Jackson was being treated as a witness, Sgt Woodbridge said.
"He's a witness at this stage, because he was the only person in the house when the fire started, so we need to speak to him as a witness and see where that leads us."
Meanwhile, a Givealittle page established by Mary-Jane Kirkman, of Oamaru, had raised more than $700 for the family by yesterday afternoon.
Dunedin residents were also rallying to support the family.
Moyle's Fresh Choice Green Island supermarket acted as a drop-off point for donations, and within hours a car-load of goods was heading north.
Ms Nelson said yesterday her partner had also lost everything in the fire, and she had just broken the bad news to her two young girls, aged 6 and 10.
Ms Nelson thanked emergency services and the community for their help.
She and her family were planning to leave town for a break.
"We are just blown away, just blown away by the generosity of everyone - it's amazing.
"We just need a few days break to be with family and grieve really for what we've just lost."
- Oamaru police (03) 433-1400, Crimestoppers 0800 555-111.
