Five people died and three others were hospitalised after toxic gas erupted inside a factory restroom in the city of Hebi, central China's Henan Province, local authorities said on Tuesday.

The incident took place at Hexin Chemical Industry Co. in Shancheng District, where a sulphuric acid storage tank is believed to have leaked, sending acid into the plant's storm-water system and then into a septic tank, where it reacted to produce hydrogen sulphide gas.

One of the injured remains in serious but stable condition, while the other two sustained minor injuries, according to the district’s emergency management bureau.

Operations have been halted, and all personnel have been evacuated from the site. A full investigation is now in progress.