The incident occurred during "routine work" at a liquid-waste treatment workshop in Suzhou, Catcher spokesman James Wu said, according to The Wall Street Journal. Catcher builds unibody metal cases for Apple's MacBook lineup, and also supplies components to other companies such as Dell and HTC.
Of the employees that are injured, three are said to be in serious condition, while one has reportedly been transferred out of intensive care. The factory where the incident occurred was previously given a worst-possible "black" rating by the Suzhou Municipal Environmental Protection Bureau.
The incident comes after Apple initiated a strong crackdown on its overseas supply chain, following criticism asserting that Apple's devices are assembled by workers who earn low pay and operate in unsafe working conditions.
Earlier this year, Apple became the first technology company to request independent audits of its overseas supply chain from the Fair Labor Association. Initial inspections from the FLA found a number of violations at Foxconn, Apple's assembly partner.
Apple's unibody manufacturing process was detailed in this 2008 video.
This week's incident at a Catcher plant isn't the first time an employee has died on the job at a Chinese plant of one of Apple's partners. Two workers were killed at a Foxconn iPad assembly plant in 2011, while a handful of employee suicides at Foxconn's facilities also gained international attention.
This March, Apple Chief Executive Tim Cook himself visited a Foxconn iPhone plant in Zhengzhou, China, to see first-hand the facility. That visit came after a series of reports on Apple and Foxconn stirred up debates about labor rights in China.
For years, Apple has also conducted its own internal audits of its overseas supply chain. The latest report, issued in January, found no intentional underage labor in 229 audits, a marked improvement from the 49 underage workers Apple discovered in its audits released in 2011.