Rescuers have launched a massive search for more than 400 people, many of them elderly Chinese tourists, who are missing after a cruise boat was hit by a freak tornado and capsized on the Yangtze River in what may become China's worst shipping disaster in nearly 70 years.

Battling bad weather, divers and other rescue workers pulled five people they found trapped in the upturned hull of the four-deck Eastern Star, a small fraction of the 458 people on board when the ship capsized on Monday night.

Distraught relatives of some of the passengers scuffled with officials in the city of Shanghai, where many of those on board had booked their trips, angry about what they said was a lack of information.

Dozens of rescue boats battled wind and rain enveloping the southern section of Asia's longest river to reach the ship, which lay upturned in water some 50 feet deep.

|Rescuers could hear people calling for help from inside the ship's hull and television showed rescuers cutting through it with an angle grinder.

One of the people pulled from the capsized boat was a 65-year-old woman. Divers fixed breathing equipment to her nose and mouth to bring her up from under the water.

About another dozen people had been rescued and six bodies recovered, leaving more than 430 people unaccounted for.

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.

A passenger manifest said those on board the Eastern Star ranged in age from three to more than 80.

Tour guide Zhang Hui, 43, said the boat sank very quickly and he scrambled out a window in torrential rain, clutching a lifejacket as he could not swim.

"Wave after wave crashed over me; I swallowed a lot of water," Mr Zhang said. He was unable to flag down passing boats and finally struggled ashore, clinging to a branch, as dawn broke.

President Xi Jinping had ordered no efforts be spared in the rescue and Premier Li Keqiang went to the scene of the accident.

About 60 family members gathered outside a travel agency in Shanghai and demanded information.

"I only found out about this on the television news while I was at work and I came here," said 35-year-old Wang Sheng, whose 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."

The ship's captain and the chief engineer, who were among the few to be rescued, had been detained by police for questioning.

According to the Yangtze River navigation administration, the pair said the ship went down quickly after being caught in the tornado.

Initial investigations had found the ship was not overloaded and it had enough lifejackets on board for its passengers. Those rescued were wearing lifejackets.

Among those on board were 406 tourists, many of them elderly, along with 47 crew members and five tour guides.

The ship was said to have capsized in about two minutes and no distress call was issued.

Fishing boats were among the dozens of vessels helping in the search and rescue and more than 1,000 police with 40 inflatable boats had also been sent.

The Eastern Star, which has the capacity to carry more than 500 people, was heading to the southwestern city of Chongqing from Nanjing, capital of Jiangsu province. It sank at around 9:28 p.m. in the Jianli section of the Yangtze.

Accidents of this magnitude are uncommon in China, where major rivers are used for tours and cruises. A tug sank on the Yangtze while undergoing sea trials in January, killing 22 of 25 people on board.

In the worst previous incident of its kind in China, the steamship Kiangya blew up on the Huangpu river in 1948, killing more than 1,000 people.