What we know about the fatal Hunter Valley wedding bus crash

Forensic and traffic police are piecing together the events of a fatal bus crash in NSW's Hunter Valley, which has claimed the lives of at least 10 wedding-goers.  

The bus has been left in situ after flipping at a roundabout while en route to Singleton at 11:30pm last night, as investigators scour the site this morning.

Acting Assistant Commissioner Tracy Chapman said 10 people had been confirmed dead, but more fatalities were "possible".

A total of 25 people were taken to hospital with "varying injuries", she said, and officers are yet to discover if more bodies are trapped underneath the wreckage.

The bus diver, a 58-year-old man, has been arrested and police expect to lay charges.

The bus remains on its side after overturning at a roundabout. (ABC News)Where did it happen?

The bus overturned at a roundabout on Wine Country Drive as it was entering the Hunter Expressway in Greta, about 50 kilometres north-west of Newcastle.

Police understand the passengers were travelling to Singleton after attending a wedding at Wandin Estate at Lovedale, in the Hunter's popular winery district.

The estate is about 10 kilometres away from the roundabout where the crash unfolded.

"Our investigation and information at this stage indicate that it is a single-vehicle collision but obviously as we work through that scene and obtain any other information that's available from witnesses or from what the scene presents, then we will look at all avenues," Acting Assistant Commissioner Chapman said.

"I understand they had been at a wedding together. It's my understanding they were travelling together to Singleton, presumably for their accommodation."

In a statement, Wandin Estate's management said they were "deeply saddened" by the event and that the venue would be closed for Monday.

How many people were injured?

There were more than 30 people on board at the time of the crash.

Police have confirmed 10 deaths and say that number could rise.

Acting Assistant Commissioner Chapman said 25 people were transported to hospitals in Newcastle, Maitland and Sydney, including two flown to Royal Prince Alfred Hospital.

It was possible other passengers might be trapped under the bus, the senior police officer said.

"I probably couldn't elaborate on whether it will or not, but certainly the bus is still on its side and yet to be righted and there are also people who are still injured in hospital, at least two of which were airlifted and so there's always a possibility that that number may increase."

Local residents leave flowers near the crash site.(ABC News: Keely Johnson)

The ages of the passengers are unknown but there are no reports of children being on board.

She also would not elaborate on the nature of injuries sustained by the survivors.

"If there are friends or family of anyone who may have been on that bus: we are still trying to identify all of the people on the bus, they can contact Cessnock police station," she said.

What caused the crash?

Investigations into the incident are still at an early stage and Acting Assistant Commissioner Chapman did not divulge specific details about what might have caused it.

She declined to comment on whether speed could have been a factor, saying it was "far too early" to tell.

There was heavy fog in the region at the time of the single-vehicle crash.

The bus driver was taken to hospital for mandatory testing last night and is now under arrest at Cessnock police station.

Acting Assistant Commissioner Chapman expected charges would be laid against the 58-year-old man.

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

"There's sufficient information … for us to establish that there will be charges, but I won't go into the detail about those at this stage."

Acting Assistant Commissioner Tracy Chapman called the incident a tragedy.Calls for information

Police are urging anyone with information about who was on the bus or the crash itself to come forward.

Acting Assistant Commissioner Chapman said it was a "very confronting" scene for first responders and a tragic event for the community.

"The number of family members, but broader community, who will be impacted by this, you couldn't count.

"From a policing perspective, our role is to make sure that we undertake a full and thorough investigation to ensure that some comfort may be given to those family members and the public at the conclusion of that investigation and that process."

Family and friends of a person who may have been on board the bus are urged to call Cessnock police on 02 4991 0199.

Witnesses — or anyone with information relevant to the circumstances surrounding the crash — should contact Crime Stoppers.

Seventh-worst road accident on record

The Hunter Valley bus crash is the worst road accident since 1994.

With at least 10 people killed in the crash at Greta overnight, it ranks equal seventh with a crash between a semi-trailer truck and a bus at Wangaratta, Victoria, on Melbourne Cup Day in 1993.

The worst road accident was the Kempsey bus crash in December 1989 where 35 people died.

Two months before that, a head-on collision between a tourist coach and a truck in Grafton killed 21 people.

The last road accident to have more than 10 people killed was at Boondall in Queensland in 1994.