A bus driver at the wheel during one of Australia’s deadliest crashes is facing allegations of manslaughter after the charges against him were upgraded.

Brett Andrew Button, 59, was driving a bus carrying 35 wedding guests when it flipped and crashed in the NSW Hunter Valley shortly before midnight on June 11 last year.

Nine passengers were killed at the scene and another died on the way to hospital.

Button was initially charged with 10 counts of dangerous driving and one count of negligent driving causing death when he appeared in Cessnock Local Court in June.

But the bus driver has been hit with a series of extra charges, including 10 counts of manslaughter for those killed in the crash and 16 counts of furious driving causing bodily harm.

Button now faces 89 charges in total.

He is accused of driving dangerously fast in thick fog and telling passengers to “fasten your seatbelts” moments before losing control of the vehicle at a roundabout.

The bus smashed into a guard rail before tipping and crashing on its side.

Button is out on conditional bail. He will face court again on Wednesday.

The community of Singleton was hardest hit by the disaster, with seven locals among the 10 people killed.

A junior doctor, a husband and wife and a mother and daughter were among those who died while returning from attending a wedding at the Wandin Estate Winery in Lovedale.

-AAP