Hong Kong (CNN) -- At least 36 people have died after two passenger boats collided off Hong Kong's Lamma Island on Monday evening, throwing more than 100 people into the sea.
The crash happened on a night when Hong Kong's busy waters were even more crowded than usual, as the city celebrated China's National Day.
One of the vessels, owned by The Hong Kong Electric Company, was carrying company employees and their families to watch the scheduled fireworks display when it was struck by a passenger ferry traveling from Hong Kong Island to Lamma.
Government officials said the collision occurred off Lamma's coast at around 8:20 p.m. local time.
"I thought we'd hit a rock or a lighthouse," said Chris Head, a school teacher who was on the passenger ferry that crashed into the Hong Kong Electric vessel.
He said the force of the impact threw him out of his seat at the back of the ferry, which was not very full of people.
As the damaged ferry began to move toward the pier in the small town of Yung Shue Wan on Lamma, Head said he could see the other boat had started to sink into the water vertically, like the Titanic.
According to the Hong Kong Fire Services Department (FSD), which led the rescue, the vessel sank quickly after the impact. It said low visibility and many obstacles on board made it difficult for rescuers.
The FSD said its rescue boats, including a diving support vessel, arrived on the scene at 8:41 p.m. local time and managed to pull 123 people from the water.
Twenty-eight people were declared dead at the scene, and eight others were certified dead upon arrival at the hospital, according to a statement early Tuesday from the Hong Kong government. The survivors were taken to five hospitals around the city, with nine said to have serious injuries, the government statement added.
"After 10 minutes out a boat crashed into ours from the side at very high speed," one male survivor told the South China Morning Post. "The rear of the ferry started to sink. I suddenly found myself deep under the sea. I swam hard and tried to grab a life buoy. I don't know where my two kids are."
Residents on Lamma reported being woken up in the middle of the night by the massive rescue operation going on offshore.
On Tuesday, the front of the stricken vessel was still sticking out of the water, tethered to a big barge just a few hundred meters from Lamma. Police vessels surrounded the scene, and divers were conducting a search.
The authorities have not ruled out the possibility that some people may still be inside the vessel or missing.
The passenger ferry was able to dock safely. Government officials have not yet confirmed if passengers aboard that vessel were injured, but Head said nobody around him appeared to have been hurt.
The narrow sea lanes leading into Hong Kong's main deepwater harbor are some of the busiest in Asia, with giant commercial freighters, ocean liners, passenger ferries and private boats of all sizes sharing the same waters.
Hong Kong is home to more than 200 outlying Islands, including Lamma, which lies to the southwest of Hong Kong Island -- the city's financial center. Hong Kong Island is located to the south of Victoria harbor, with Kowloon forming its northern shores. To the north of Kowloon lie the New Territories, which stretch all the way to mainland China.
CNN's Judy Kwon, Jethro Mullen, Pamela Boykoff and Mark Morgenstein contributed to this report.