LANZHOU, Nov. 18 (Xinhua) -- Several staff of a metal smelting company in northwest China's Gansu Province have developed symptoms of poisoning, authorities said Saturday.

Four employees of Gansu Zhaojin Precious Metal Smelting Company checked into the Lanzhou University Second Hospital on Monday and Tuesday. Doctors suspect they were suffering from arsine poisoning. The patients showed symptoms of numbness in the arms and legs, nausea, vomiting, and abnormally colored urine. They were in critical condition and were put under intensive care.

On Friday, another four employees of the company checked into the hospital. According to doctors at the hospital, three of the four new patients appeared to be suffering chronic arsine poisoning. The patients are currently in stable condition.

The company was established in 2012. It is located in Lintao County.