Samsung forces employees at its Chinese factories to work up to five times the legal overtime limit, bans them from sitting down and denies basic labor rights, according to a US-based watchdog.

According to China Labor Watch's probe of eight factories, the South Korean electronics giant is guilty of widespread "legal and inhumane violations."

These include forcing workers at the Tianjin Samsung Mobile Display factory to put in as many as 189 hours of overtime in a month, when the legal limit is 36 hours, according to a report released in New York.

Employees at the factories, making consumer products including cell phones, televisions, and refrigerators, regularly stand for 11 to 12 hours while working at a frantic pace, the 122-page report said.

For example, employees at the Suzhou Samsung Electronics Company facility have to assemble a nearly meter (three-foot) long panel and install two screws every nine seconds, while workers at Tianjin Intops, a supply factory, have to assemble a cell phone case every five seconds.

If workers wish to complain about mistreatment, they have no one to turn to, the report said.

"Workers lack any effective grievance channel by which to rectify these transgressions," China Labor Watch said.

The group probed six Samsung factories and two Samsung supplier plants by sending undercover investigators and interviewing employees outside the workplace.

There was no immediate response from Samsung. However, the Seoul-based corporation earlier on Tuesday responded to a separate report from China Labor Watch alleging that children under the age of 16 are employed at a supplier, HEG Electronics in Huizhou.

Samsung said it would inspect its nearly 250 Chinese partners.

"We are implementing a rigorous plan to address any potential violations," the company said in a statement, vowing to terminate contracts with any Chinese suppliers in violation of labor norms.

The on-site inspections will be carried out by a 100-member team by the end of September, it said.

Initial audits conducted by Samsung found HEG employed teenaged student workers and interns, but none younger than 16, the company said.

However, it did uncover a system of fines for lateness and absence -- banned in China -- as well as excessive overtime and inadequate health and safety standards.

According to China Labor Watch's new report, those types of practices are in fact widespread.

At four factories, workers "are forced to work overtime. Even if not forced, workers often have no choice but to work overtime because their base wages are too low to support themselves," it said.

Safety is given insufficient importance, according to the report, citing the case of workers at the Tianjin Intops plant "who come into contact with printing fumes (but) don't receive or wear protective masks."

At the same time, Samsung and its partner factories insist on what China Labor Watch calls "unfair or simply cruel" rules.

These range from counting sick days as work absences to strict rules about personal appearance, with Huizhou Samsung Electronics "reported as refusing to hire any person less than 1.55 meters (five feet) tall or that has tattoos, dyed hair, or physical disabilities."