A fire which left two people in hospital with serious burns may have been started inadvertently by some residents allegedly sniffing butane gas.
Police say they are treating the blaze, at the guest house in the centre of St Austell late on Saturday night, as suspicious.
A total of 15 people were evacuated from Trevanion Lodge in Trevanion Road, following a small explosion.
Eight people were treated for smoke inhalation, while two were treated by paramedics at the scene for burns before being taken to the Royal Cornwall Hospital at Truro.
The pair were last night still being treated at the hospital, where their injuries are described as serious but not life threatening.
Inspector Andy Oliver, of Devon and Cornwall Police, said an investigation was underway and the fire was being treated as "suspicious."
"At this time we are investigating the cause of fire in connection with the fire brigade," he said.
"One line of inquiry that is being followed up is that the fire might have been caused inadvertently by two males reportedly sniffing butane gas in a room prior to the explosion.
"Two males remain in a serious condition in hospital with burn injuries. At this time the injuries do not appear life threatening."
Suzy Cooper, manager of Trevanion Lodge, which describes itself as a family run B&B, said it had been a "traumatic" event but they were thankful lives had not been lost.
"We have been saying that it could have been so much worse," she said. "All our fire procedures were in place and we acted quickly and it saved everyone in the building."
She said the contents of one room were "disintegrated" but from the outside the fire door had remain intact and stopped the blaze spreading.
Mrs Cooper said the B&B hoped to reopen shortly, but until then it was closed, which was a double blow for their clients.
"We have got to shut off part of the building," she said.
"We offer emergency housing for homeless people so with this fire they have been made homeless again, which is awful for them.
"We hope to be open again within 24 hours. It's just going to be a lot of hard work."
Eighteen firefighters from St Austell and Mevagissey battled the blaze on the first floor of the property after the alarm was raised at around 11.20pm.
Initial reports that people were trapped in the burning building proved unfounded.