17/02/2017 7:20 AM AEDT | Updated 17/02/2017 11:10 AM AEDT

Three Found Dead Inside Water Tank In Rural NSW

Police have confirmed that the victims are family members and include a husband and wife.

Three people have died in an in-ground concrete water tank in rural NSW, after a 69-year-old man working in the tank collapsed and died and two people coming to rescue him also perished.

While police are still investigating, the cause of the deaths at the rural property on Thursday evening are believed to be the result of carbon monoxide poisoning.

Relieving Commander Andrew Koustoufis of Hume Local Area Command told reporters on Friday that the male had been conducting routine maintenance of the tank using a high-pressure water pump fuelled by petrol, which it is believed to have caused the build up of deadly fumes.

"As a result [he] collapsed at the bottom of the water tank and was followed in by his 68-year-old brother," he said.

"As a result of going down into the tank, the 68-year-old brother collapsed and has also passed away."

Emergency services were called to the property on Thursday evening.

In what has been described as an absolutely tragic set of circumstances, the 69-year-old's wife, aged 63, then followed into the water tank and also passed away.

"We can't confirm cause of death at this stage [but] carbon monoxide poisoning is a line they are following," Koustoufis said.

Prior to entering the enclosed tank, the 63-year-old woman is believed to have contacted a neighbour who called emergency services to the property.

It is believed that the bodies of the three victims were only removed from the tank this morning, with the retrieval process being delayed due to the presence of high levels of poisonous gas.

"There was a whole host of officers from a range of emergency services that responded...they did a wonderful job in response to a nasty incident," Koustoufis said.

A brief is currently being prepared for the coroner as the small country town of Gunning is left devastated.