SHANGHAI, Feb. 12 -- About 300 employees of a Shanghai electric firm required medical attention on Wednesday morning for reasons unknown, local authorities said.

According to a statement from the Jiading district government, 299 employees from Higgs Electric (Shanghai) Co.,Ltd, based in the district, felt sick and went to hospital around 1 a.m..on Wednesday. Symptoms included headaches, fever and diarrhea, according to sources with Ruijin Hospital affiliated to Shanghai Jiao Tong University.

As of 5 p.m., nine people remain hospitalized in stable condition.

Investigation is underway.

Established in 2011, the company has 531 employees.