In 2008, a speeding bus careered out of control at a Sai Kung roundabout, leaving 18 people dead and 44 injured.
The dead included 17 men and two women, police said.
According to injured passengers, the bus was allegedly going faster than allowed after they had complained that the bus was 10 minutes behind schedule, local media reported. The injured are being taken to hospitals across Hong Kong and rescuers are still trying to release people trapped inside.
Multiple passengers interviewed by the TVB and Cable TV news channels said the bus was moving at a high rate of speed when the accident happened. "It was like the tyre slipped, and the bus turned".
"It was much faster than I normally feel on a bus", he said.
Saturday's accident appears to be the worst since July 2003, when a double-decker fell off an elevated road after being hit by a lorry, killing 21 people.
KMB general manager Godwin So Wai-kei said the 30-year-old unidentified driver joined the company in 2014 and had driven the route before.
Godwin So Wai-kei, general manager of Kowloon Motor Bus Company Limited which the bus belonged to, said the company will offer 80,000 HK dollars (10,256 USA dollars) as a condolence allowance for the families of each victim.
She said the commission will be headed by a judge and she expected it to come up with suggestions to ensure Hong Kong's public transport system is reliable and safe.