Eighty people were injured early Friday when a high-speed ferry travelling from Hong Kong to Macau hit an "unidentified object" in the water, according to Hong Kong's marine department.
"Information received from the Marine Department suggested that 80 people on the ferry were injured. Among them four were classified as seriously injured," a spokesman for the Hong Kong government told AFP.
It comes just a month after Hong Kong marked the one year anniversary of a sea collision which claimed 39 lives, the city's worst maritime disaster for over 40 years.
Friday's accident happened at around 1:20 am (1720 GMT) near one of Hong Kong's small outlying islands Hei Ling Chau, the spokesman said.
There were 105 passengers and 10 crew members aboard, with no reports that anybody was missing, he added.
"There was suddenly a loud bang. The ferry was thrown upwards. Then many passengers were thrown out from their seats," one passenger, named as Mr Wong, was quoted as saying by Hong Kong's Apple Daily news website.
After the accident the ferry sailed back to Hong Kong Island's downtown Sheung Wan terminal where a dozen of ambulances were waiting to tend to the injured, he said.
RTHK news website showed a passenger on a stretcher surrounded by emergency staff. A government spokesman said there were no further details on passengers' injuries.
Local television footage appeared to show the ferry being towed back to the terminal.
"We only know that it sailed back but how it did so we are not sure," a government spokesman said.
The safety of Hong Kong's waters was called into question after the fatal October 1, 2012 crash which saw the Lamma IV launch -- carrying more than 120 people -- collide with the high-speed Sea Smooth ferry near Lamma Island.
The launch was carrying employees of the Hong Kong Electric utility and their family members and friends to watch a fireworks display to celebrate China's national day.
A subsequent inquiry found a "litany of errors" contributed to the accident.
It described how the bow of the Sea Smooth crashed into the main passenger cabin on the Lamma IV, crushing people as water rushed in. The launch partially sank within two minutes.
The two captains have each been charged with 39 counts of manslaughter and are awaiting trial.
The tragedy shocked the Asian financial hub, one of the world's busiest ports, which prides itself on its good safety record.
The marine department has tightened inspections to ensure boats meet safety requirements including adequate lifejackets and watertight fittings.
