SYDNEY: At least 10 people died and 25 were injured after a chartered bus carrying wedding guests rolled off a ramp at a roundabout in the Hunter region in Australia's New South Wales (NSW) state, police said on Monday.

The accident occurred around 11:30 p.m. (1330 GMT) on Sunday near the town of Greta, about 180 km (112 miles) northwest of Sydney, in an area famous for its vineyards and wedding spots.

"I understand they had been at a wedding together, it's my understanding they were travelling together ... presumably for their accommodation," NSW Police Acting Assistant Commissioner Tracy Chapman said during a televised media briefing.

At this stage, it appeared to be a single-vehicle accident, Chapman said. Police were still trying to identify all the passengers, she said. Some people could be trapped beneath the bus, which was lying on its side.

The driver of the bus, a 58-year-old man, was under arrest and expected to be charged over the accident. He had been taken to hospital for mandatory testing.

Heavy fog was present in the area at the time but the cause of the accident had not been determined, Chapman said.

The two worst bus accidents in New South Wales state were head-on collisions within two months of each other in 1989 that killed 35 and 21 people each. Eighteen people died in 1973 when a tourist bus plunged down a slope after a brake failure.

Prime Minister Anthony Albanese expressed his "deepest sympathies" to the families of the people killed and injured.

"All of us know the joy of going to a wedding ... they are some of the happiest times that you can have. For a joyous day like that in a beautiful place to end with such terrible loss of life and injury is so cruel and so sad and so unfair," Albanese told reporters.

The Wandin Valley Estate winery which hosted the wedding was closed on Monday, a public holiday, the Australian Broadcasting Corp reported.

"We are deeply saddened to hear of the bus crash overnight that has claimed the lives of some of our guests," ABC reported, citing a statement from the vineyard.