Hong Kong's chief executive Carrie Lam said she was "deeply saddened", after visiting one of the 12 hospitals that were treating the injured.
Rescuers cut open the top of the bus to save the passengers trapped inside.
"The latest figures ... include 17 male and two female", a government spokeswoman said, adding "we are still counting the number of injuries".
Carrie Lam, Hong Kong's top official, said after the crash previous year that she didn't believe new laws governing drivers' hours were an answer, and that any solution had to address broader questions of worker shortages.
Authorities say dozens more are injured after the bus flipped over in the southern Chinese city. "And then it was like the tyres skidded, and the bus overturned".
The injured have been rushed to hospitals, while the site of the accident has been cordoned off. It was really chaotic in the bus.
While bodies of dead passengers were laid out on the ground, covered in white sheets. The fire brigade responded at 6.15pm.
Police told Xinhua earlier that 19 people were killed but the death toll was later revised down to 18.
In 2003, 21 died and 20 were injured in the worst road traffic accident in Hong Kong history when a KMB double decker bus crashed through a guardrail and down a hill off Tuen Man Road after colliding with a truck.
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