No casualties have been reported, according to the county government. A fire that erupted after the explosion has been brought under control, officials said.
The controversial chemical plant was built in 2009 on Gulei Peninsula after the project was called off in the coastal city of Xiamen amid protests over potential pollution and health problems, state-run Xinhua news agency reported.
A Zhangpu county government spokesman said an initial investigation found that a cracked hydrogen pipeline triggered the fire during a pressure test.
He said the blast did not heavily damage the plant, nor has it resulted in any chemical leaks.
This is the second explosion of a chemical plant in the last few days.
A massive explosion destroyed a chemical factory in the city of Liaocheng in China's eastern Shandong Province on July 27. Official media said no casualties were reported in that blast.