The Sewol ferry left the Port of Incheon two hours late on Tuesday night, waiting for a veil of fog to lift, easing the craft's journey southwards.
The craft was about half full. Of the 462 passengers aboard, 325 of them were students from a high school in Ansan city, near Seoul. Fifteen teachers were escorting them on a four-day trip to Jeju island to see the wonders of the volcanic formation, the waterfalls and lava tubes nestled by the country's tallest peak.
There are faster ways to get to Jeju, but many people take the ferry because it is cheaper than flying. Many South Korean high schools organise trips for students in their first or second years, and Jeju is known as a popular destination.
The boys and girls aboard were second-year students, most of them aged 16 or 17. They had settled in for a 14-hour journey.
After breakfast, passenger Kim Seong-mok said he felt the ferry tilt. Then he heard the vessel hit something.
Cha Eun-ok said she was on deck taking photographs. "The ship went 'boom' and there was a noise of cargo falling," she said.
The boat was a few kilometres off the shore of Byeongpung island.
The area was clear of fog, unlike further north up the coast, which had been shrouded in heavy fog that led to the cancellation of many ferry services.
Watch: Families face agonising wait after Korean ferry tragedy
YTN TV said that the craft had barrelled into rocks.
A crew member on a government rescue ship said the area was free of reefs or rocks and the cause was likely a malfunction.
The operator made an announcement: passengers should not move from their places, Kim and Cha said.
At 8.58am local time, three hours from its destination, the Sewol sent a distress call to the coastguard. By then the ship was already listing to one side, according to the Ministry of Security and Public Administration.
The craft shook and tilted, sending students on each of its floors careening into one another, said student Lim Hyung-min. Some of the students were bleeding.
Luggage and vending machines crashed down on passengers as the vessel tipped, another student said.
From the decks, the students made their own choices.
Lim jumped. So did many of the other passengers.
"I was so cold,'' he told a reporter. "I was hurrying, thinking that I wanted to live."
Water quickly rushed into the ship's passages.
The vessel's severe tilt kept them from reaching the exits, Kim said. Some people urged those who couldn't get out of the ferry to break windows.
More than 80 vessels and 18 aircraft swarmed the stricken ship. Rescuers clambered over the boat's sides. Several passengers had donned life jackets and the rescuers hustled them into steel baskets that were winched up to hovering helicopters. Navy Seals arrived.
Terrified passengers wearing life jackets clambered into inflatable boats as water lapped over the ferry's rails.
Some aboard slid down the inclined side and plunged into the water. Rescuers, including the crew of what appeared to be a small fishing boat, struggled to pull them to safety.
Rescuers plucked 179 people from the boat and the water, 55 of whom were injured. They were brought - wet and many without shoes - to nearby Jindo island, where medical teams wrapped them in pink blankets and checked them for injuries before settling them down on the floor of a cavernous gymnasium hall.
Within a few hours only the Sewol's blue-and-white bow could be seen above the waves. Soon, that too had disappeared.
At least six people were confirmed dead.
An official from the Mokpo Hankook hospital on the mainland said one student had died soon after arriving at its emergency ward.
A female crew member also perished. The coastguard said one person had been found dead inside the sinking ferry.
By nightfall nearly 300 were missing - likely trapped inside or floating in the ocean. Such a high number raised fears that the death toll could rise drastically. South Korea's biggest ferry disasters happened in 1993 when 323 people died.
The water temperature was cold enough to cause hypothermia after about 90 minutes to two hours of exposure, said an emergency official who requested anonymity.
Officials said mud on the ocean floor made underwater search operations difficult.
Passenger Kim told YTN that he was "certain" that many people were trapped inside the ferry as water quickly rushed in and the severe tilt of the vessel kept them from reaching the exits. Some people urged those who couldn't get out of the ferry to break windows.
A total of 178 divers were searching the submerged vessel, said Lee Gyeong-og, Vice Minister of Security and Public Administration.
The US 7th Fleet said an amphibious assault ship, the USS Bonhomme Richard, which was on routine patrol west of the Korean peninsula, was being sent to provide help.
"There is so much mud in the sea water and the visibility is very low," Lee said. Strong currents also hampered the rescuers.
The Sewol had lived up to its name. The name means time and tide in Korean.
Associated Press, Bloomberg, Reuters
The death toll from past ship disasters in Asia
An estimated 4,341 passengers died, with just 24 surviving, when the Dona Paz collided with an oil tanker in the Philippines on December 20, 1987.
As many as 3,920 died when passenger steamship Kiangya blew up and sank in the mouth of the Huangpu River, China, on December 4, 1948.
A Japanese passenger ferry sank in Typhoon Marie on September 26, 1954, killing an estimated 1,153 people.
More than 800 people are believed to have died when the Princess of the Stars ferry went down off the coast of San Fernando, Philippines, on June 21, 2008.
A fire on board sank the Tamponas II in the Java Sea, Indonesia, killing 580 passengers on January 27, 1981.
On June 29, 2000, 491 people perished when an overloaded ferry carrying refugees from the Maluku Islands in Indonesia sank in a storm.
Between 400 and 500 people are believed to have drowned when the Indonesian ferry Senopati Nusantara sank in the Java Sea during a storm on December 30, 2006.
Typhoon Unsang sank the Dona Marilyn, killing 389 passengers, as it sailed from Manila to Tacloban in the Philippines on October 24, 1988.
South Korea's deadliest ferry disaster came in 1970 when 323 passengers were killed, officials said. Another accident claimed 292 lives in 1993.
At least 108 people are believed to have died when the Thomas Aquinas passenger ferry collided with a cargo ship on August 16, 2013 while on its way to Cebu in the Philippines.
Thirty-nine people were killed in Hong Kong when the Lamma IV collided with a passenger ferry and sank while taking Hongkong Electric employees and their families to watch the National Day fireworks on October 1, 2012.