The deaths of a woman and her elderly parents at a caravan park in Cornwall have been described as an "appalling tragedy".
The victims are all believed to have died of suspected carbon monoxide poisoning.
The alarm was raised at the park near Camborne just before 1pm after the couple's helper was unable to reach them, Devon and Cornwall Police have said.
Firefighters were called to break into the static caravan at Tremarle Home Park, North Roskear, and found the bodies of three people, and a dog, inside.
The woman was aged in her mid-40s. The age of her parents is not yet known.
Inspector David Eldridge of Devon and Cornwall Police said: "Shortly before 1pm this afternoon, we were called to a caravan park near Camborne in Cornwall, where a helper had been unable to get a reply from an elderly couple who lived in the caravan.
"We were able to see that there was a figure sat in a chair but they were unresponsive to knocks at the door.
"Cornwall Fire and Rescue were called. They forced entry into the property and found that the three occupants were all dead."
An investigation into what caused the deaths is under way, but the incident is not being treated as suspicious.
A Cornwall Fire and Rescue Service spokesman said a crew from Camborne Community Fire Station attended the scene with a hazardous materials advisor after being called at 12.56pm.
Camborne Town Council member David Biggs described the deaths as an "appalling tragedy".
"Tremarle Park is a residential caravan site and has provided homes for people for many years. It's a well established facility and is very well run. It was a shock to learn that three people have died there."
Stephanie Trotter, president and director of the independent charity CO-Gas Safety, said carbon monoxide was an incredibly lethal gas.
"Less than 2% of CO (carbon monoxide) can kill in between one and three minutes. It cannot be sensed using human senses of smell, touch, sight or hearing," she said.
"The Department of Health estimates that about 40-50 people die of CO and about 4,000 attend Accident and Emergency every year in England and Wales alone."
Mrs Trotter added: "We are very sorry to read of these tragic deaths. We send sympathy to family and friends and offer free, confidential help and advice."
The Health and Safety Executive said it would not be investigating as the incident took place at a domestic address.