HONG KONG—More than 80 passengers were injured when their Macau-bound high-speed jetfoil collided with an unknown object just west of Hong Kong's Victoria Harbour.

The Hong Kong government said at least three of the 85 people who were sent to hospitals were in serious condition. Most passengers suffered injuries from the force of the impact.

The ferry, operated by Shun Tak-China Travel Ship Management Ltd., was carrying around 105 people en route to the gambling mecca of Macau from Hong Kong when the collision happened at about 1:20 a.m. Friday local time, the government said. Local television footage showed many passengers being carried into ambulances on stretchers after the ferry was towed back to port.

The ferry operator said the jetfoil, which is equipped with radar, was traveling at its normal cruising speed of 38-40 knots (43-46 miles per hour). It said it was unclear what the ferry collided with in the pitch dark of night, and added there was no visible damage to the jetfoil. The operator also said it was likely the seriously injured passengers weren't wearing seat belts, which are installed on all seats.

The Hong Kong-Macau ferry route is one of the busiest in the world, with jetfoils plying the one-hour journey as frequently as every 15 minutes during the day. Services are around the clock. Other high-speed ferries also crisscross Hong Kong's waters to the city's outlying islands as well as to cities in mainland China.