Dozens of angry relatives of those missing in China's cruise ship disaster clashed with authorities in Shanghai Wednesday, demanding answers and to be taken to the scene of the tragedy on the banks of the Yangtze.

Many of the passengers were elderly tourists from the eastern part of the country, and as hopes for finding more survivors fade two days after the disaster, their families have grown increasingly distraught.

As Chinese authorities threw up an exclusion zone around the site of the Eastern Star which sank Monday night with some 450 aboard, relatives desperate for news massed outside Shanghai's main government building.

Video shared on social media showed the group confronting uniformed police outside the building, pushing and shouting. An unidentified man fell to the ground during the melee.

"The police first formed a human wall and didn't let us in. Then the relatives got excited and started to shout. Some policemen hit people," said one young woman whose mother was on the boat.

The police led the group inside the building and then bussed them to a government-designated reception centre, a cavernous room where other tearful relatives were glued to a television airing live coverage of the rescue effort.

"The policemen lined up to form a path leading to the bus. That was the only way to leave," one relative who gave his surname as Zhang told AFP.

- 'We need to know' -

At the reception centre in Shanghai, the nation's commercial hub, frustrated families complained bitterly about the lack of information and begged to be taken to see the upturned vessel.

"We need to go to the site. That's our common appeal," said the mother of seven-year-old Yang Chenlin who was on the boat with her grandparents.

"No matter whether she is dead or not, we want to know and we need to see her body," the girl's maternal grandmother Xu Naixiong said.

At the centre, a petition was circulating with demands for more information and access to the site.

Chong Ye, whose 55-year-old father and 53-year-old mother were on the boat, said the relatives were being stonewalled.

"Waiting here is no use at all," he said. "It's already two days. No news has come out. I just want to know how my parents are. Why can't the government at least tell us this?"

Authorities took away one man who confronted police at the centre, but he later said he had been quickly released.

"I'm ok. The police didn't make it difficult for me," he posted to social media.

At the scene of the disaster in central China, authorities strictly controlled access to the scene of the capsize, where rescue boats were clustered around the upturned hull of the Eastern Star.

Just 14 people have been rescued, including some hauled out of the wreckage with the help of breathing equipment, while another 19 bodies have been recovered, according to state media.

Near the stretch of river in Jianli in Hubei province, authorities were strictly enforcing roadblocks about two kilometres (1.2 miles) from the ship, and turning back media attempting to reach the scene.

China's Communist Party leaders are sensitive to the handling of disasters, and the reaction from relatives, as any missteps or delays can lead to criticism of their effectiveness to govern.

The government commonly clamps down on organised gatherings or collective expressions of anger as it seeks to enforce stability.

Family members of the Chinese passengers on board missing Malaysian Airlines flight MH370 have been particularly vocal, and say they have faced harassment from authorities in their own country as they seek answers on the aviation mystery.

The Yangtze disaster has come at a sensitive time, a day before the anniversary of the June 4 crackdown on the 1989 pro-democracy movement, when the government imposes tight control on any sign of dissent.