Media playback is unsupported on your device Media caption The ferry was operating at normal speed when the incident occurred, the BBC's Juliana Liu reports

About 85 people have been injured, six of them seriously, when a high-speed ferry hit an "unidentified object" in Hong Kong, officials say.

A government spokesman told the BBC that the accident happened at 01:20 local time (17:20 GMT Thursday) near the island of Hei Ling Chau.

The boat was travelling from Hong Kong to Macau. The operator said it had 105 passengers and 10 crew on board.

The vessel was later towed to a local terminal, reports said.

"There was suddenly a loud bang. The ferry was thrown upwards. Then many passengers were thrown out from their seats," one passenger was quoted as saying by Hong Kong's Apple Daily news website.

There were no reports of any people missing, and an investigation is now under way.

Image caption The Madeira did not appear to have suffered major damage

Fire officers launched a search at the scene of the collision, but could not locate the unidentified object, local media reported.

"The object involved might have been broken into pieces and sunk or drifted away," one fire officer told journalists.

In a statement, ferry operator TurboJet identified the boat as the Madeira.

"The vessel has been escorted back to Hong Kong Macau Ferry Terminal. Preliminary check revealed no significant damage on the vessel body," it said.

"The company will co-operate closely with the authorities to investigate the cause of the incident," the statement added.

A spokesman for the company that operates the ferry has been quoted as saying most passengers were probably not wearing their seat belts, the BBC's Juliana Liu in Hong Kong reports.

The spokesman added the vehicle was not speeding, and there was no obvious damage to the boat, our correspondent says.

Transport accidents resulting in fatalities are extremely rare in Hong Kong.

Last year, 39 people died when a pleasure boat and a high-speed ferry collided off Hong Kong's Lamma Island.

The captains of the two vessels were charged with several counts of manslaughter and a report into the crash said "systemic failings" in the marine department contributed to the accident.