The bus was carrying a lot of passengers when it overturned on a highway in the suburbs.
Hong Kong has undergone a tragedy of losing nineteen lives with 40 others injured after a double-decker bus crashed.
The accident was the city's deadliest bus incident in almost 15 years. Police have arrested the driver and charged him with causing death by unsafe driving.
The man said he managed to get out of the bus by himself.
Photos and videos published by social media showed the gold-coloured bus lying on its side with its roof torn off, while emergency workers treated injured passengers nearby.
Early reports said the number of dead stood at 19 but that was later revised down.
The injured have been rushed to hospitals, while the site of the accident has been cordoned off.
A spokesman from the bus company, The Kowloon Motor Bus company, said HK$80,000 (£7,300) would be paid to each victim's family.
Representatives from the bus operator said on Saturday evening that the driver had a good track record and knew the route, which only runs on race days. So far there is no sign of fatigue driving when the accident occurred, said the general manager.
The safety of Hong Kong's waterways has also remained under scrutiny since 39 people were killed when a high-speed ferry and a pleasure boat crashed in 2012.
Hong Kong's public transport is usually safe, and deadly accidents of this scale are relatively infrequent.
In September past year, three people were killed when a double-decker bus mounted a pavement in Sham Shui Po.