The bus was carrying passengers returning from a wedding on Sunday when it overturned at a roundabout near the town of Greta in New South Wales (NSW).
Many of the victims are connected to tight-knit rural sporting clubs, local media have reported.
The crash is one of Australia's deadliest road incidents.
Brett Andrew Button, 58, has been charged with multiple counts of dangerous driving and negligence, after being arrested on Monday.
He was allegedly driving "in a manner that was inconsistent with the conditions", the NSW Police Traffic and Highway Patrol Commander told reporters on Tuesday.
"He lost control of that vehicle... obviously the speed was too quick for him to negotiate that roundabout," Acting Assistant Commissioner David Waddell added.
Fourteen people injured in the crash in the Hunter Valley wine region remain in hospital, with two in a critical condition, police say.
They have not formally identified any of the victims, but the mayor of Singleton said many lived in the small town.
"I know we'll never get over it," Sue Moore told the BBC.
Some local families have been at the side of injured people in hospital in Newcastle and Sydney, Ms Moore said, and others are planning funerals while reeling from "the worst possible thing that could ever happen in their lives".
"As far as I know, one lot of parents are leaving two kids orphaned," she said.
A junior doctor, Rebecca Mullen, was among those killed, said NSW Health Minister Ryan Park."This has made a very dark day even darker for NSW Health," he said.
Tasmanian man Kane Symons also died in the crash, his former surf club confirmed on social media.
Posting on behalf of his family, the Carlton Park Surf Lifesaving Club described Mr Symons as "an amazing athlete... a great bloke and a mate to many".
"We adored him and he will be truly missed," they said.
Pop-up mental health clinics have been set up in Singleton and the nearby town of Cessnock to support the local community, and Ms Moore said discussions are under way to fundraise for the victims' families.
Mr Button is also a Hunter Valley local, and is clearly hurting along with the victims' relatives, a magistrate said when he faced court on Tuesday morning.
"I see before me a man suffering," Magistrate Robyn Richardson said, granting him bail.
The Cessnock Local Court heard Mr Button had committed seven driving offences over the past 30 years, but did not have a criminal record.
Prime Minister Anthony Albanese on Tuesday said the "horrific tragedy" had rocked the country, particularly because people "associate weddings with love and... celebrations".
"Of course, the scars will last for such a long, long period of time," he told the Australian Broadcasting Corporation.
The crash site was "still an active crime scene", police said on Monday, with forensics officers working through the wreckage.
The Hunter Valley in NSW is known for its vineyards and native bushland, making it a popular spot for wine lovers and group outings or celebrations.
