The food factory in Changning County, Yibin of Southwest China's Sichuan Province where a suspected gas poisoning incident took place. Photo: Hongxing News

A suspected hazardous gas poisoning incident at a food factory in Southwest China's Sichuan Province on Monday afternoon has left seven people dead as of 10 am on Tuesday.

"The clinical manifestations of the dead reveal that they may have died of hydrogen sulfide poisoning," a doctor who treated the patients said, according to CCTV.

The food factory specializes in processing bamboo shoots. 

The incident happened during a facility maintenance procedure in a food factory in Changning County, Yibin of Sichuan Province, according to a notice issued by the county authority on Weibo on Monday evening.

The incident is still under investigation, the notice said.

A staff member of the Shuanghe township government where the food factory is located told the Global Times on Tuesday, "The food factory is currently under lockdown. The police, medical staff and firefighters are all at the scene. It is not yet clear how long the lockdown will last."

A local person familiar with the incident said that several people collapsed as they went to the factory to help, as cited by Hongxing News.