A man who caused one of Australia's worst crashes is set to enter the witness box

Brett Button is facing a sentence of years in prison after his dangerous driving tipped a bus full of wedding guests - killing 10, in June last year.

The 59-year-old, who's pleaded guilty, is expected to give evidence in Newcastle District Court today.

Witnesses have told the court Button was showing off before the crash, ignoring passengers' pleas to slow down.