China's Foxconn manufacturing sites are expanding based on cheap labor, while Japan's older, traditional Sharp plants hang on through cost-cutting measures.
Foxconn workers are blaming company security guards for Sunday's unrest at a manufacturing facility in China.
Apple supplier Foxconn reopened a manufacturing facility in China on Tuesday a day after it closed following a mass riot involving 2,000 workers.
Apple supplier Foxconn said an "incident" involving 2,000 workers erupted late Sunday night near a company manufacturing facility in China, as photos posted online showed cars turned over and store windows broken in what appeared to be a mass riot.
A Foxconn worker was found dead on Wednesday morning, with Chinese press calling it a suicide, but authorities are still investigating.
Apple supplier Foxconn has denied forcing vocational school students in China to work at its factories.
A labor rights group has accused Samsung of "illegal and inhumane violations" at its factories in China, reporting cases of excessive overtime and exhausting conditions.
China's smartphone shipments surpassed those of feature phones for the first time ever during the second quarter.
Foxconn, a major supplier to Apple as well as other tech companies, has been steadily improving the working conditions at three of its Chinese factories following a February audit, according to the Fair Labor Association.
The number of lawsuits against Apple in China continues to grow: A Taiwanese man has sued the company, alleging that the FaceTime feature on its iPhone and iPad infringes on one of his patents.
A Samsung supplier in China allegedly employs workers under the age of 16, according to a labor watchdog group, which found the student workers earn about US$1 an hour.
A Taiwanese university has sued Apple for alleged patent infringement in its Siri voice assistant, in retaliation for patent disputes brought against Taiwanese firms by foreign rivals.
Apple's revenue for China saw robust growth in its fiscal third quarter, as iPhone sales continued to boom, even though the company delayed the launch of its new iPad in mainland China.
Apple's new iPad went on sale in China on Friday morning with a sparse, but orderly, line of people at one of its stores in Beijing, as the company used a new reservation system.