Officials say QF32 hit turbulence and took a plunge over the Indian Ocean. Passengers had just a few seconds warning to get to their seats, so not everyone was buckled in when things got bumpy.
"It's like going in a speedboat and hitting a wave very fast, and you kind of go flying over the wave. It felt a bit like that. Everything went flying high in the air," said one passenger.
Some passengers reported cuts on their heads, while others broke bones.
The plane landed in Singapore safely and remained for 24 hours while engineers made checks and passengers were treated. The flight returned to Sydney on Sunday night.
ABC News contributed to this report.