Ten people have died in a wedding party bus crash in Australia's Hunter wine region in New South Wales, police said on Monday, announcing the arrest of the 58-year-old driver.

The light-coloured coach lay on its side after the accident, with a dozen emergency workers wearing high visibility yellow vests nearby in the foggy night, television images showed.

The toll may yet rise, with 25 passengers taken to hospital – two of them airlifted from the crash by helicopter, said Acting Assistant Commissioner Tracy Chapman.

Police were not aware of any children being involved, she said.

The coach driver was subjected to mandatory testing at hospital, the police officer told reporters at the scene.

"He's under arrest. He's been the driver of a motor vehicle collision where there have been fatal injuries and there will be charges pending," she said.

The passengers had been at a wedding together, the officer said, and were presumed to have been heading to their accommodation after the festivities.

"All Australians waking up to tragic news from the Hunter send our deepest sympathies to the loved ones of those killed in this horrific bus tragedy," Prime Minister Anthony Albanese said.

"For a day of joy to end in such devastating loss is cruel indeed. Our thoughts are also with those who have been injured," he said in a message on social media.

The area is being examined by specialist forensic police and a Crash Investigation Unit.

The Hunter region north of Sydney is replete with vineyards, kangaroos and native bushland, making it a popular spot for tourists and group outings.

A local mayor said the bus was travelling from a wedding reception, held at a nearby wine estate.

"We are still waiting for further details to come to light" Jay Suvaal, the mayor of nearby Cessnock, told ABC. "It does appear that it was a wedding chartered bus." (AFP)