Thousands of workers went on strike Friday, Oct 5 at a Foxconn plant in central China that makes Apple Inc's iPhone 5, paralyzing production of the smartphone, the rights advocate group China Labor Watch said, according to Reuters.

The reported strike comes at a crucial time for the U.S. corporation, weeks after kicking off its largest-ever global rollout of the smartphone. Apple is already struggling with supply constraints, analysts say.

Citing workers, the labor group said 3,000 to 4,000 workers began their strike at Foxconn's Zhengzhou complex in central China in the afternoon, angered by over-exacting quality controls as well as demands they work through the week-long National Day holidays, which began on Monday.

The strike could not be immediately confirmed, and nor was it clear whether the stoppage was over or continuing. Some Chinese media carried reports of the China Labor Watch account, but did not offer any verification.

Apple declined to comment. A Foxconn spokesman said the company was "gathering facts" on the reported strike and would issue a statement when ready, Reuters says.

The Watch did not mention in its release when work might resume.

Foxconn Technology Group of Taiwan, the trading name of Hon Hai Precision Industry Co, is the world's largest contract maker of electronics for global brands such as Hewlett Packard Co, Nokia and Dell Inc.

Apple and Foxconn have come under fire for poor working conditions and wages at plants across China. In response, they have organized an audit of factory conditions, raised wages, improved safety and reduced overtime, among other measures.