'Please come back'
Many of the passengers aboard the ship were students of Ansan Danwon High School on a four-day trip to the resort island of Jeju.
At the school in the suburb of Seoul, parents sat on mats, clutching their cell phones for calls or texts from their children.
Local media reported on several text messages they said were from passengers. In one, a passenger describes women screaming in the darkness. In another, a father learns his child is trapped. In a third, a son, fearing death, tells his mother he loves her.
CNN could not independently confirm the authenticity of the messages or when they were sent. It's also unclear what happened to the people who sent them.
The panicked messages were reason enough for some parents to believe more survivors will be found.
On one wall of the school, officials have posted a list of names. Once a confirmation of a rescue came, they circled that name. On Wednesday, soon after the ship sank, several names were circled in rapid succession.
So many, however, remain untouched.
At one point Wednesday, the school announced that all students had been rescued but soon backtracked, to the parents' wrath.
Even though the school was closed Thursday, students and teachers arrived to seek comfort in numbers.
"Please be alive," said messages written in classroom chalkboards. "Please come back."
On Thursday, several parents took a boat to try to go the accident site. The boat turned back after several of them became so distraught that they fainted.
The five-story passenger ferry, Sewol, was carrying 475 passengers -- most of them students -- as it left from the port city of Incheon, just west of Seoul, for a trip to Jeju, the resort island considered the Hawaii of Korea.
Foggy weather had delayed the departure by about two hours.
Just before 9 a.m. Wednesday (8 p.m. Tuesday ET), about 12 miles from the island of Jindo, the ship ran into trouble.
Passenger Kim Sung-Mook told YTN he was eating breakfast in the ship's main hall when he felt the ferry begin to tilt.
Someone made the announcement telling passengers to stay in place. Then, Kim said, he heard a loud bang.
Student Lim Hyung Min, who was rescued, told YTN he heard the bang before the ship began to list.
"The students were falling over and crashing into things and bleeding," Lim said.
Ret. Capt. Jim Staples told "AC 360" that the ship's captain may have increased speed to remain on schedule.
Mary Schiavo, former inspector general for the Department of Transportation, thinks the ship could have hit something.
The ship's operator, Chonghaejin Marine Co., had no explanation -- only apologies.
"We deeply apologize to the families, and I'm saying once again we're really sorry," Chonghaejin executive Kim Young-bung said.
"Our company will promise that we will do our best not to lose any more lives."