At least 67 people were killed when a platform collapsed at a construction site in China's Jiangxi province.
Only two workers were rescued alive and a third was still missing, state television said.
The accident took place at a power plant in Fengcheng where a cooling tower was under construction.
Industrial accidents are common in China, prompting calls for better safety standards. Last year, 170 people died at a chemical blast in Tianjin.
Jiangxi province's fire services said some 32 fire trucks and 212 soldiers had been deployed in the rescue efforts.
Photos posted by Chinese media showed iron pipes and concrete slabs lying on the ground inside the large cooling tower.
Recurring tragedy: By Carrie Gracie, BBC China editor
Sensitive to a Chinese public which is increasingly intolerant of lax safety standards, the government sent a senior official from the capital to supervise the investigation, and said those responsible for the disaster would be held accountable.
But the disasters and the government promises now follow a familiar pattern and China's record on industrial safety remains grim. In the first half of the year alone more than 14,000 Chinese workers died in factories, mines and on construction sites.
Even as China grows richer, corner cutting dogs its workplaces. Partly the problem is aggressive competition, partly corruption. But the absence of strong unions to fight for worker protection does not help. Nor a heavily controlled media culture which discourages whistle blowers.
Last year China's president promised his government would learn lessons paid in blood after a chemical blast killed 170 people. But the accidents keep coming and without more independent scrutiny of workplaces, it is hard to see that changing.
According to Jiangxi Daily, two 168m cooling towers were being built at the site as part of a project to add two 1,000-megawatt coal-fired power units to the power plant.
The project will cost 7.67bn yuan ($1.11bn; £890m).
Chinese Premier Li Keqiang ordered an investigation, demanding that those responsible for the accident should be held accountable, Chinese media reported.
It added that the State Administration of Work Safety dispatched a team to investigate the causes of the accident.