The samples of 591 workers in south China's Guangdong Province are under medical test after 23 of their fellows in the same workshop have been diagnosed as suffering from mercury poisoning, local health authorities said Tuesday.

Medical personnel with the Guangdong Prevention and Treatment Center for Occupational Diseases collected the urine samples from workers of the T8 workshop of the Foshan Electrical Lighting Co., Ltd from Dec. 18 to 20, said Yang Aichu, director of the center's outpatient department.

By mid-December, the company's 23 workers on production lines using liquid mercury were found having excessive mercury in their urine after spontaneous body checks in the municipal or provincial prevention and treatment center for occupational diseases, said Lu Ruijin, the company's human resource manager.

Some of the victims showed symptoms such as headache, hair loss, joint aches and trembling, Lu said.

"I never wore the mask the company offered me, because I felt uncomfortable with it," said a 55-year-old worker, Jiang Enqing.

Mercury poisoning is often caused by inhalation of mercury vapor and dust of mercury compounds. For lighting companies, adoption of solid mercury can effectively reduce the risk of poisoning, Yang said.

So far, the company has applied solid mercury on 80 percent of its production lines. It has shut down five remaining ones using liquid mercury in the T8 workshop and planned to transform them by the end of January next year, Lu said.

It also promised to cover the examining fees for all its employees including the 23 workers who had body checks on themselves, and pay their salaries during treatment.