The dam burst following a weekend of unseasonal weather that battered eastern Australia.

Snow fell, gales lashed the coast, knocking down trees and power lines, and crops were extensively damaged in a bout of unseasonal weather that brought an icy chill to eastern Australia.

Rockhampton police said that emergency service personnel have this morning found the body of the four-year-old Blackwater girl, who was washed down the Mackenzie River when an inflatable rubber bladder on the Bedford Weir, near Blackwater, burst.

Search crews located the girl's body at around 6.20am, approximately 800 metres down stream from the weir.

According to police, it is believed the girl had been visiting the weir with her mother and two adult friends when the accident occurred around 4.30pc yesterday.

All four were swept away by the influx of water, but an SES flood boat was only able to rescue the three adults last night, with one of the women found clinging to a tree.

Three men walking along the weir wall were also swept away and rescued by the SES.

Meanwhile, Orange, NSW, was expected to be declared a natural disaster zone after snowfalls obliterated millions of dollars' worth of hail netting and uprooted orchards, while roads between Bathurst and Oberon were closed as 10 centimetres of snow fell around the Blue Mountains.

A spokesman for the NSW Bureau of Meteorology said the chilly spell was caused by cold air, originating from Antarctica, moving up the NSW coast, delivering cold winds through southern Queensland as well.

Tim Hall, a fruit farmer near Orange, said his property had more than $300,000 in damage caused by more than 10 centimetres of snow and strong winds that flattened dozens of fruit trees.

He said he had never seen anything like it, and neither had his neighbours.

Officers from the Department of Primary Industries will view the damage during the week to assess if affected property owners will be eligible for natural disaster assistance.