Rescue operations on a capsized Chinese cruise ship extended late into Tuesday night as workers battled to find more than 400 people still missing after the boat sank in the storm-tossed Yangtze river.

A total of 15 people have so far been saved from the Dongfangzhixing, or "Eastern Star," which went down late Monday on the popular tourist route from the eastern city of Nanjing to the southwestern city of Chongqing, the official Xinhua News Agency reported. Earlier, rescuers freed three people who were trapped from the ship's wreckage.

According to the AFP news agency, six bodies have also been recovered from the wreckage, but hundreds more are still missing after the passenger ship apparently sank in a matter of seconds, according to state media. Many of the passengers are believed to be elderly Chinese tourists.

Chinese media reports cited Prime Minister Li Keqiang, who had travelled to the site of the wreckage, as saying he had approved a rescue plan involving the cutting of the ship's hull to free trapped passengers on Wednesday. Rescuers had avoided cutting the hull on Tuesday as they feared that would allow air into the vessel and speed up the sinking. Cranes will also be deployed to aid the rescue efforts on Wednesday.

Reuters reported that paramilitary vehicles, dozens of police and soldiers as well as medical and meteorological trucks were surrounding the site of the wreckage. Soldiers set up periodic roadblocks along a muddy path, allowing only official vehicles into the area in the central province of Hubei.

At the main hospital in the county of Jianli, police guarded the door of a room where survivors were being treated and blocked reporters from trying to enter. Three survivors were placed in the general ward while the rest were in intensive care, according to a nurse.

China's weather bureau said a tornado had buffeted the area where the boat was passing through, a freak occurrence in a country where twisters can happen but are not common.

Xinhua reported earlier that rescuers could hear people calling for help from inside the four-deck ship which capsized in a storm late Monday night. CCTV showed pictures of rescuers on the hull listening for sounds of life.

State broadcaster CCTV showed rescue workers carrying an elderly woman on a stretcher who was covering her own face. Xinhua said a 65-year-old woman was pulled from the boat on Tuesday afternoon and CCTV described her as in "good physical condition".

Dozens of rescue boats battled wind and rain to reach the ship, which lay upturned in water about 15 metres deep.

Xinhua on Tuesday evening said the number of those on board were 456, down from earlier reports saying the ship was carrying 458 people. Those on board included 405 passengers, 46 crew members and five travel agency workers.

Most passengers on board the cruise liner were aged over 60, according to a manifest cited by the Nanjing-based Oriental Guardian newspaper. Many were on a tour organised by a Shanghai travel agency.

Citing the Yangtze River navigation administration, Xinhua reported that those rescued included the ship's captain and chief engineer, who said the vessel sank quickly after being caught in a cyclone.

The captain and the engineer have been detained by police for questioning, according to Reuters.

About 60 family members gathered outside the travel agency on Tuesday to demand information, some of whom scuffled with officials. Some family members of the crew of the ship waited outside Chongqing Eastern Shipping Corporation which owns the capsized vessel.

The company operates tours along the Three Gorges area along the Yangtze river.

"I only found out about this on the news while I was at work and I came here," said 35-year-old Wang Sheng, who said his mother and father were on board. "I cried all the way here and here I can't find anyone, the door is locked."

Another relative, Wang Yiping said her father was on the boat and that relatives had gathered at the Shanghai district government office with several dozen other relatives of passengers.

"He went on the trip with his friend," Wang said, sobbing. "He left on May 28. When he had time, he would go out to travel with a bunch of friends."

President Xi Jinping has ordered that no efforts be spared in rescue work, while state broadcaster CCTV earlier showed Mr Li at the scene looking through binoculars and giving instructions. Mr Li had also chaired a meeting to direct the rescue and emergency response work, where he said that saving lives should be the top priority, according to Xinhua.

The Ministry of Transport and China National Tourism Administration were also ordered to mobilise all resources available to speed up the search and rescue work and help treat those saved. More than 1,000 armed police with 40 inflatable boats had already been sent to the site, Xinhua said.

The Eastern Star was heading to south-west China's Chongqing city from Nanjing, capital of eastern Jiangsu province. It sank at around 9:28pm local time in the Jianli section of the river. No distress call was issued, with the ship sinking within two minutes, state radio reported.

Seven people had swum to shore to raise the alarm, the People's Daily said.

Xinhua reported that initial investigations had found the ship was not overloaded and it had enough life vests on board for its passengers. Those rescued were wearing life vests, Reuters reported citing Xinhua.

Chinese netizens reacted with shock at the tragedy with many offering their prayers, hopeful that the passengers might still be alive. The capsize was the top trending item on Weibo, a Twitter-like microblog.

Weibo user "lingzhiyi" said: "Let's not let the Korean boat tragedy repeat itself in China. Let's make every effort to rescue everyone on the ship."

Added user "xizu": "Yet another calamity has happened, we can only hope that the heavens are merciful, to bless and protect the safety of more people."

Additional reporting by Agence France-Presse and Reuters