The Eastern Star capsized late Monday in stormy weather as it carried 458 passengers -- mostly senior citizens -- and crew members along a stretch of the Yangtze that winds through central China's Hubei province, authorities said.
By Tuesday night, only 15 survivors and five bodies had been recovered, state media reported, as rescuers battled darkness and rain in a desperate effort to reach those trapped inside the wreck. The survivors included the ship's captain and chief engineer, who were taken into custody for questioning.
Divers plunged into the river and rescue workers gathered along part of the vessel's upturned hull that was sticking out of the water.
They used hammers to knock on the body of the ship, which was almost completely submerged, and heard responses from inside, a state-run local newspaper reported. Welders used blowtorches in an attempt to cut the hull open.
More than 1,000 armed police officers, equipped with 40 inflatable boats, were participating in the rescue effort, said Xinhua, the Chinese state news agency.
Images of the upended ship evoked memories of the Sewol, the South Korean passenger ferry that sank last year, taking the lives of more than 300 people, most of them high school students.
In this case, the majority of the 406 passengers on the cruise were between 50 and 80 years old, according to a list published by state media. The youngest was 3.
There were also 47 crew members and five travel agency workers on board, according to state media. All of those on board were reported to be Chinese.
Unless many more people are rescued, the Yangtze River sinking will become the deadliest passenger ship disaster in Asia since the Sewol went down.
Ship capsized during storm
The Eastern Star had been making a multistop journey up the river from Nanjing to Chongqing, a city hundreds of kilometers inland. River cruises along the Yangtze are popular among both Chinese and international tourists.
The Yangtze is the third-longest river in the world, stretching 6,300 kilometers (3,915 miles) from its source in the mountains of Tibet all the way to the East China Sea.
The ship capsized around 9:30 p.m. Monday during a storm over the section of the river that flows through Hubei's Jianli County, authorities said.
The captain and the chief engineer, who made it off the ship alive, both said the ship had been hit by a longjuanfeng, a Chinese word that can be translated as cyclone or tornado, Xinhua reported.
But Zhang Zuqiang, a senior official with the China Meteorological Administration, told the newspaper Beijing News that he wasn't sure there had been such a storm. But it was raining heavily at the time, he said.
Alarm raised by survivor
Local authorities launched rescue efforts after receiving a phone call from a survivor who managed to swim ashore, according to Chinese media.
The sunken ship is now about 3 kilometers (1.9 miles) from the shore, where the river is around 15 meters (50 feet) deep, China's state-run broadcaster CCTV reported.
Relatives were desperately seeking news.
Yan Mao told CNN that his mother, aunt and two cousins were on the ship after boarding it at Nanjing, the eastern Chinese city where the multiday river cruise began Thursday.
Yan said he was on his way to Wuhan, a major city roughly 150 kilometers from the area where the ship is reported to have gone down.
"I am anxious to find them," he told CNN. "Of course, I believe they are alive, otherwise I wouldn't go there."
Yang Min, a Shanghai resident whose parents and child were on the ship, said he was anxiously waiting with many other families for updates at a local government office in the city.
Premier arrives at site
Chinese Premier Li Keqiang and other senior officials arrived Tuesday at the site of the disaster to oversee the large-scale emergency response.
To help with the rescue effort, authorities reduced the amount of water being discharged from the Three Gorges Dam, the world's largest hydroelectric plant, which is upstream from the sunken ship, state media reported.
More than 4,000 people and 110 vessels have taken part in the search and rescue, Chinese Transport Minister Yang Chuantang said at a news conference. Divers have been called in from all around the country, he said.
A CNN team saw scores of military trucks and buses on an expressway heading toward the site of the sinking. Each one was packed with soldiers wearing orange life vests.
Debate on social media
Chinese social media users weren't waiting for the results of any official investigation before launching into a debate on whether to blame humans or the bad weather for the disaster.
"What could the captain have done?" asked one top-rated comment in a popular conversation thread on Weibo, a Twitter-like microblog service in China.
But another top-rated comment wanted to know if pre-emptive measures could have been taken: "How could meteorologists not have forecast the weather situation? If they did, why didn't they notify those in charge of the ship?"
China's deadliest passenger ship disaster in recent memory is believed to be the capsizing of the ferry Dashun off the coast of eastern Shandong province in 1999. That sinking killed 282 people, according to authorities.