More than 100 rescuers clawed through the rubble of a six-storey building housing a cinema and guesthouse.
President Xi Jinping gave instructions to free those trapped in the debris “at all costs”.
Emergency teams rescued five of the 23 people inside when the structure partially collapsed, sending up a huge cloud of dust in the city of Changsha on Friday.
At a news conference, it was announced the survivors are in stable condition in a hospital.
Another 39 people, present around the site when it toppled, remain uncontactable.
Media footage showed rescuers carrying a person into an ambulance late on Friday and communicating through rubble with those who remained trapped.
After the collapse, worried friends and relatives took to social media seeking help to find missing people, including students from Changsha Medical University, who they had lost contact with.
Southern Metropolis News quoted the operator of a restaurant in the area as saying a funeral was being held downstairs before the incident.
Preliminary investigations revealed that the building also housed several apartments, a restaurant on the second floor, a coffee shop and a hotel, state broadcaster CCTV reported.
The tenants had made structural changes to the premises, and the exact cause of the collapse is still being investigated, the report said.
Following an increase in the number of self-built building collapses in recent years, Xi also said that it was necessary to check on such structures to investigate any hidden dangers and fix them in a timely manner to prevent the occurrence of major accidents, according to state-run news agency Xinhua.
Photos showed the front of the building largely intact, while the rear section appeared to have collapsed into itself.
Poor adherence to safety standards, including the illegal addition of extra floors and failure to use reinforcing iron bars, is often blamed for such disasters in China.
In January, an explosion triggered by a suspected gas leak brought down a building in the city of Chongqing, killing more than a dozen people.
Twenty-five people also lost their lives in June 2021 when a gas blast hit a residential compound in the city of Shiyan.