JINDO, South Korea — The parents waited in dread through the night, huddled under blankets in this South Korean port town, staring out to sea for a sign that rescuers had found any of the 281 people, many of them high school students, still missing after a ferry sank on Wednesday.

They refused to sleep in a tent set up for them, preferring to scan the horizon for helicopters returning from the rescue effort 11 miles off the country’s southwest coast. As the hours passed with little news of what may be one of South Korea’s worst peacetime disasters, they demanded information from officials who said that fierce tides were keeping divers from entering the ship, which had mostly slipped beneath the waves long before.

“Why are you not going in to save them?” one woman screamed. Another, Chung Hae-sook, the mother of a missing 16-year-old boy, echoed her rage: “There is no tomorrow for this,” she said. “My heart is turning to ashes.”

By Thursday morning, the Ministry of Security and Public Administration, which is coordinating the rescue efforts, reported that 175 passengers and crew members had been rescued. Nine people were confirmed dead, including four students, two teachers and a member of the ferry’s crew. But fears of a much higher death toll were stoked as survivors said they believed that many people had been trapped below deck. According to some who spoke to the local news media, passengers had been told to remain in their seats and may have stayed there until it was too late.