Rescuers have cut a 55 cm by 60 cm rectangular hole on the bottom of the overturned ship, Eastern Star, in a desperate measure to give divers easier access to the hull.
The rescuers will continue to cut through the hull while the divers comb the 76-metre ship for more than 370 people still missing, state-run Xinhua news agency reported.
Rescuers retrieved another 39 bodies till this morning, bringing the death toll to 65.
Premier Li Keqiang travelled to the disaster site in the central Hubei province county of Jianli to monitor the rescue efforts.
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But information about the accident has been strictly controlled and officials gave few details on the progress of the recovery efforts.
Meanwhile anxious relatives of the passengers missing after the mishap became restive, as four days have passed and wanted to go to the site of the shipwreck.
In Shanghai, some grieving families even clashed with authorities, demanding answers.
Questions remain over why the ship made a sudden turn 10 minutes before capsizing and whether a tornado recorded in the area at the time of the accident had directly hit the ship, Hong Kong-based South China Morning Post reported.
The ship's captain and chief engineer, who both survived, are in police custody.
"If the voyage data recorder [the black box of the ship] shows the captain made the turn in the stormy weather instead of losing control [after the ship was hit by strong winds and tides], it would be fair to say he bears responsibility for the tragedy," Professor You Qinghua, from Shanghai Maritime University was quoted as saying by the Post.
He said this was done only to meet updated standards from the shipping authorities, news website The Paper reported.
The ship was carrying 405 passengers, five tour guides, and 46 crew members.