Major flooding hit parts of Australia's east Friday, stranding thousands of residents, prompting a military airlift and leaving some communities only accessible by helicopter.

The deluge, which has sparked dozens of rescues and left about 7,275 people isolated in various parts of New South Wales state has also impacted Queensland to the north where some regions have been declared a natural disaster zone.

"From the air it looks like an inland sea," New South Wales Premier Barry O'Farrell said after visiting the region.

Evacuations have been ordered from some houses and businesses in the New South Wales town of Moree, where more than 600 people registered with an evacuation shelter as the Mehi River peaked, the State Emergency Service said.

"The town of Moree is inundated with water -- so north Moree is not only cut off, but many of the properties there are flooded," O'Farrell said.

"As you fly over the centre of the town there are streets that look like canals that have more relevance to Venice than north western New South Wales."

A Royal Australian Air Force C-130 Hercules aircraft was moving bedding to Moree, as locals sandbagged buildings against the Mehi and rising Gwydir river as the water hit levels not seen in decades.

In Queensland, the inland town of Roma was cut off by floodwaters which are threatening scores of homes and expected to more further west towards Charleville on Saturday where there were fears whether the levy would hold.

As the crisis deepened, unprecedented floodwaters isolated an evacuation centre in the Queensland town of Mitchell, forcing authorities to relocate about 300 people who had taken shelter there.

"The waters are still rising and we've already seen it exceed the previous record (from) some time in the 1800s," Queensland Premier Anna Bligh said.

"These are very, very difficult circumstances for the people of this town."

Bligh said Mitchell's hospital had also been evacuated and five schools closed amid fears the Maranoa river could reach a record level of 10 metres (33 feet).

In New South Wales, the Mehi river has now peaked but the water is expected to remain for several days and authorities have warned of the dangers of floodwaters.

"It's a huge logistical operation with a major flood," SES Deputy Commissioner Steve Pearce told the Seven Network.

"There have been some circumstances where we've had to use one if not all of our 18 helicopters to airlift people out of some isolated areas.

"Fortunately most people abided by those evacuation orders."

The floods come just over a year after massive floods deluged much of Queensland and northern New South Wales, swamping mines and farmland, wiping out entire hamlets and bringing the city of Brisbane to a watery standstill.

As the rains continued, Moree mayor Katrina Humphries said while her town was well prepared, there was no telling when the downpour would end.

"Mother Nature has her way and she'll stop crying when it suits her," she said.