Three children and one woman have been found dead by relatives when they returned to their Ashburton home today.
Police said it was understood the four people found dead late this afternoon had been house-sitting for relatives living at the Thomson St property in the suburb of Tinwald.
Police Mid-South Canterbury area commander Inspector Dave Gaskin said the relatives were talking to police at the station.
The deaths were being treated as suspicious, he said.
"They actually came home and found the bodies in the house. We're still treating the death as suspicious until we can ascertain exactly what happened.
"There's no obvious indication of foul play, but obviously it's a pretty fluid situation at the moment."
Insp Gaskin said the scene is likely to be guarded overnight and the bodies would be retrieve tomorrow.
An officer initially on the scene about 4pm thought he smelled an "odour" inside the house like gas, causing police to believe that LPG might have been involved.
Emergency services were called to the house and firefighters were seen entering the property wearing breathing apparatus. A hazardous chemicals vehicle remained at the property tonight.
Police had been doorknocking houses on the stretch of cordoned-off Thomson Rd between Manchester Rd and Wilkin St, checking in with neighbours to see if they smelled gas and if they were feeling okay.
Residents were asked to stay inside while investigations continued.
Jeremy McKenzie said his mother lives near the property where the group was found. Police had asked her whether she had smelled gas and had asked her to stay indoors. It was an upsetting situation, Mr McKenzie said.
A neighbour who lives about four doors down from the house said the first vehicle on the scene was an ambulance just before 4pm, followed by a large emergency response with at least two fire trucks and five police cars.
The Fire Service was initially called to the address for a cardiac arrest, but it is understood they were met by police who said there were four people found dead.
