State media showed fire fighters -- backed by a digger -- cutting through a morass of metal and sheets of concrete, while rescuers shouted into the tower of debris to communicate with any survivors.
A crowd gathered as chains of rescuers removed pieces of brick by hand, allowing experts a deeper look into the pancaked building.
Some of the injured were rushed on gurneys through a narrow alleyway late on Friday, while sniffer dogs combed the area for further signs of life.
No cause for the disaster has yet been given by authorities, although speculation turned to possible overwork on the property, which officials said was eight storeys high, correcting earlier reports that it was six.
"Tenants had made structural changes to the premises to varying degrees," state broadcaster CCTV reported, adding that the reason for the collapse was under investigation.
Search 'at all cost'
President Xi Jinping called for a search for victims "at all cost", state media reported, adding he had ordered a thorough investigation into the cause of the collapse.
A top Communist Party official was earlier dispatched to the scene -- an indication of the severity of the disaster.
State councillor Wang Yong -- appointed by the central government -- was sent to lead a team to "guide the rescue and emergency response work", an official statement said Saturday.
Building collapses are not uncommon in China, due to weak safety and construction standards as well as corruption among officials tasked with enforcement.
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.
The same month, 18 people were killed and more injured when a fire broke out at a martial arts school, with state media reporting that all the victims were boarding school pupils.