HONG KONG (CNN) -- Hong Kong authorities announced an investigation Tuesday into the collision of two passenger boats that killed at least 38 people in the territory's deadliest ferry accident in recent memory.
The crash happened Monday evening, a night when Hong Kong's busy waters were even more crowded than usual, as the city celebrated China's National Day.
Police said they have arrested six crew members from the vessels on suspicion of endangering passengers.
Search and rescue efforts will continue for at least two more days as authorities look for missing passengers, authorities said Tuesday. They did not know exactly many are unaccounted for.
One of the two 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 Island.
Government officials said the collision occurred off Lamma's coast around 8:20 p.m., plunging more than 100 people into the water.
"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 ferry went from what felt like full speed to "an abrupt halt."
Head 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.
"It was very dark," he said. "There were very few lights on board."
According to the Hong Kong Fire Services Department (FSD), which led the rescue, the vessel began to sink quickly after the impact. It said low visibility and many obstacles on board made work difficult for rescuers.
The FSD said its rescue boats, including a diving support vessel, managed to pull 123 people from the water.
The death toll would appear to make the crash Hong Kong's most lethal maritime accident since 1971, when 88 people died after the ferry Fat Shan capsized between Hong Kong and Macau amid a typhoon.
In 2008, 18 Ukrainian sailors died in 2008 after their boat hit a Chinese cargo ship and sank.
"After 10 minutes out a boat crashed into ours from the side at very high speed," one male survivor from the accident Monday told the South China Morning Post, a local newspaper. "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, a lightly populated island to the southwest of Hong Kong Island, 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 barge equipped with a crane just a few hundred meters from the coast of Lamma. Emergency services boats surrounded the scene, and divers conducted a search.
Despite a hole torn in its bow, the passenger ferry was able to dock safely after the crash. 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, Pamela Boykoff and Mark Morgenstein contributed to this report.