The accident took place at a power plant in Fengcheng where a cooling tower was under construction.
There were a number of people still trapped at the scene, China's Xinhua news agency reported.
Jiangxi province's fire services said 32 fire trucks and 212 soldiers had been deployed.
A total of 68 people were at the construction site at the time of the accident.
According to Jiangxi Daily, two 168m-high 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.