Deadly accidents are relatively common at industrial sites in China, where anger over lax standards is growing. Three decades of swift economic growth have been marred by incidents ranging from mining disasters to factory fires.
State news agency Xinhua said 68 of the 74 dead have been identified so far, with victims ranging in age from 23 to 53.
The accident happened on Thursday morning in Fengcheng, in Jiangxi province, during work on a cooling tower for the coal-fired power plant.
The official China Daily newspaper said the accident happened when a tower crane collapsed, triggering the collapse of the entire construction platform as the night shift was being relieved by the morning shift.
"We will conduct a serious investigation into the cause of the accident and hold those who are responsible accountable," Jiangxi vice governor Li Yihuang was quoted as saying.
The company in charge of the plant, Jiangxi Ganneng Co, said in a stock exchange filing on Thursday it was cooperating with authorities.
The China Daily cited a company statement from September as saying it had started a 100-day campaign to speed up construction of the plant and take advantage of days with "fine weather".
Yang Huanning, head of the State Administration of Work Safety, had already arrived on the scene to oversee an investigation into what happened and to collect evidence, the People's Daily said.
His administration held an emergency meeting with departments all over China to learn the lessons of the accident to root out "hidden dangers" and ensure people's safety, the newspaper said.
China has vowed to improve its poor safety record.
President Xi Jinping has said authorities would learn the lessons paid for with blood after chemical blasts in the port city of Tianjin killed more than 170 people last year.
Shortly after those explosions, Yang Dongliang was removed from his post as director of the State Administration of Work Safety and later charged with corruption.
He admitted during his trial on Thursday taking bribes and gifts worth $41,00,000. He will be sentenced at a later date.
The two Yangs are not related.