A 58-year-old bus driver is under arrest after 10 people died and 25 others injured in a horrific New South Wales bus crash overnight.

The coach, reportedly carrying wedding-goers in the NSW Hunter region, rolled just after 11.30pm local time.

“He’s under arrest, he’s been the driver of a motor vehicle collision where there have been fatalities,” Acting Assistant Commissioner Tracy Chapman told a media conference on Monday morning.

“There’s sufficient information for us to establish that there will be charges pending,” she said.

Emergency services were called to the roundabout on Wine Country Drive near the Hunter Expressway off ramp at Greta and a large-scale emergency response followed, including multiple helicopters to transport the injured to hospital.

A crime scene has been established, which will be examined by specialist forensic police and the Crash Investigation Unit.

The driver was not seriously injured in the crash and was arrested at Cessnock Police Station after being released from hospital.

As of Monday morning the bus remained on its side and Ms Chapman said it was possible the death toll would increase if further people were found to be trapped under the bus or if those with injuries worsened.

An investigation into the crash has started, following a large-scale emergency response involving local police, rescue squad and highway patrol officers, ambulance paramedics, NSW Fire and Rescue, and the Rural Fire Service.

A crime scene has been established, which will be examined by specialist forensic police and the force’s Crash Investigation Unit.

No children are believed to have been involved in the crash, according to Ms Chapman.

Wineries in the area are popular with groups such as wedding parties and Cessnock City Council Mayor Jay Suvaal said chartering a bus is common.

“There will be many people from across the state and across the country that have visited our area and done the same, and I’m sure they’ll be passing on their thoughts to all those involved,” he said.

Prime Minister Anthony Albanese posted a message of sympathy on Twitter to the loved ones of those killed in what he called a horrific tragedy.

“For a day of joy to end in such devastating loss is cruel indeed,” he said.

“Our thoughts are also with those who have been injured.”

A senior NSW Ambulance officer told Seven News the magnitude of the accident had been confronting for first responders.

“Whilst they are paramedics every day of their lives, something like this is not a job that they go to every day,” she said.

“I’m incredibly proud of all the paramedics that attended. They did a fantastic job under the circumstances and no doubt they will be reflecting and we will have the right support there for them.”

Wine Country Drive remains closed in both directions at Greta, west of Maitland.

-with AAP