Five people have died and hundreds are missing after a cruise ship carrying 456 people capsized on the Yangtze River in China's Hubei province.
Officials say at least 15 people survived, with some found alive inside the submerged hull of the Eastern Star.
The captain and the chief engineer, who both survived, have been detained. They say the boat, which sent no emergency signal, was caught in a cyclone.
The rescue is continuing into the night but is being hampered by bad weather.
Chinese media quoted the captain as saying the vessel sank within minutes, while many people were asleep. BBC weather forecaster Peter Gibbs says there were severe thunderstorms in the area.
Most of those on board were tourists aged between 50 and 80 travelling from the eastern city of Nanjing to Chongqing in the south-west - a journey of at least 1,500km (930 miles).
The ship sank in the Damazhou waterway section of the Yangtze, where the world's third longest river reaches depths of about 15m (50ft).
Analysis: John Sudworth, BBC News
No doubt for some of those on the Eastern Star it would have been the trip of a lifetime.
And the Three Gorges Dam - a place of pilgrimage in its own right and a powerful symbol of China's rising economic might, attracting about two million visitors a year - now has its part to play in the rescue. The dam's engineers have been ordered to reduce the water volume flowing through the giant turbines.
The sinking of the Eastern Star will resonate widely.
A boat full of everyday Chinese tourists - from grandmothers and grandfathers down to the youngest listed passenger at just three years old - has been lost in the waters of the country's best-loved river.
At least 15 people have so far been rescued and some with minor injuries have been taken to hospital, officials said.
One survivor, tour guide Zhang Hui, told the Xinhua state news agency that heavy rain had come through cabin windows and many passengers went into the ship's hall to keep sheets and other items dry.
He said the ship then began to toss violently, to an angle of 45 degrees.
Mr Zhang said he had "30 seconds to grab a life jacket" and tried to hold on to what he could find to keep his head above water as the vessel overturned.
He clambered out of a window in the torrential rain. "Wave after wave crashed over me; I swallowed a lot of water," he said.
Mr Zhang said he heard the cries of at least a dozen other people in the water but after about 30 minutes, they all fell silent and he finally drifted into reeds and was rescued.
Three other survivors were rescued from inside the upside-down hull of the ship after it was cut open, Xinhua said.
According to the People's Daily, three bodies were recovered in Yueyang, Hunan province, some 50km away.
Some 150 boats and 4,000 emergency personnel are involved in the rescue.
Footage on state TV showed divers knocking on the submerged hull with hammers to try to make contact with trapped people.
Chinese premier Li Keqiang has arrived at the scene, according to the People's Daily.
Eastern Star - Dongfangzhixing in Chinese - had been carrying 405 Chinese passengers, five travel agency employees and 46 crew members.
The 76m-long ship weighs 2,200 tons, and could accommodate a maximum of 534 people.
The boat sank at about 21:30 local time on Monday evening (13:30 GMT), but rescuers did not reach the vessel until at least two-and-a-half hours later.
CCTV said the vessel was owned by the Chongqing Eastern Shipping Corporation which runs tours to the scenic Three Gorges area along the Yangtze.
Relatives scuffled with officials at a local government building in Shanghai, frustrated over the lack of information, Reuters reports.
They had earlier gathered outside the closed offices of the travel agency, Xiehe Travel, which made the bookings for the cruise.
They told reporters that phone calls to their loved ones on board were not getting through.
Sina News reported that a young man was seen sobbing by the door, saying: "Mum and Dad I was wrong, I shouldn't have let you go off on your holiday."
Another relative, Huang Yan, says she believes her husband and father-in-law were on board, but she could not be sure because she had not seen the official passenger manifest, the AP news agency reports.
"Why did the captain leave the ship while the passengers were still missing?'' she asked.