A collision between two passenger boats off Hong Kong has left at least 36 people dead, officials say. One of the boats was carrying more than 120 people to a fireworks display when it half-sank following Monday night's collision near Lamma Island. Twenty-eight people were pronounced dead at the scene. About 100 others have been taken to hospital, eight of whom were later said to have died. A large-scale air and sea search for survivors is still continuing. A Hong Kong government statement said: "Over 100 people were sent to five hospitals during the incident, nine of them have sustained serious injuries or are in critical condition." Rescue work would continue, the statement added, because the fire department could not rule out that there were still people inside the vessel or missing. The collision occurred during a busy period for passenger travel in Hong Kong, at the end of a long holiday weekend to mark the mid-autumn festival that this year coincides with China's National Day on 1 October. Power company Hong Kong Electric was reportedly using a commercial boat to take staff and family members to watch National Day fireworks in Victoria Harbour. The vessel and another boat - reportedly operated by Hong Kong and Kowloon Ferry - collided, causing the HK Electric vessel to list, a company official was quoted as saying. The other boat reportedly had about 100 people on board. It was slightly damaged in the crash but returned safely to port, according to Radio Television Hong Kong. A number of passengers on board were treated for minor injuries. 'High speed' Hong Kong Chief Executive CY Leung promised an investigation into the accident. "All of Hong Kong's emergency forces are focused here," he said. "Wide-ranging rescue work is being carried out on in the sea, land and in the air." Dozens of boats and two helicopters were involved in the search. The crash happened about 20:30 on Monday. Low visibility and the many obstacles on the vessel made it difficult for people to escape the listing ship, says the BBC's Juliana Liu in Hong Kong. One survivor told The South China Morning Post: "After 10 minutes out a boat crashed into ours from the side at very high speed. The rear... started to sink. I suddenly found myself deep under the sea. "I swam hard and tried to grab a life buoy," added the man. "I don't know where my two kids are." Witnesses said the boat went under very fast. "Within 10 minutes, the ship had sunk. We had to wait at least 20 minutes before we were rescued," Reuters news agency quoted one man as saying. "We thought we were going to die. Everyone was trapped inside," another woman said. Lamma lies some three kilometres (two miles) south-west of Hong Kong island, and is popular with tourists and expatriates. Hong Kong is one of the world's busiest shipping channels, but its ferries have a good safety record.