A rural NSW community is in shock after the bodies of three elderly people were found in a farm water tank.

Emergency services were called to the property on Veterans Road, Gunning, on the Southern Tablelands, at about 6.20pm on Thursday evening by a neighbour who reported the trio as having collapsed.

The two men and one women, all in their 60s, were pronounced dead at the scene.

MORE DETAILS: Three people have been found dead in a water tank on a remote property. #9News pic.twitter.com/xuLNpYfcHe

— Nine News Sydney (@9NewsSyd) February 16, 2017

It's believed that one man entered the empty underground tank before collapsing; the second man and woman followed him inside to assist him before they too passed out.

Police are expected to address the media later this morning, but The Daily Telegraph are reporting that high levels of carbon dioxide were found inside the tank, possibly from a petrol engine on a pump nearby.

The deaths are not being treated as suspicious.