Three people died and three others were hospitalized after a suspected gas poisoning incident in northwest China's Ningxia Hui Autonomous Region Saturday, the local government said.

The accident happened at a private pickle plant in Xingqing District in the regional capital Yinchuan at around 9:30 a.m., said Wu Xiaoping, deputy chief of the district government.

He said six people passed out while cleaning the pickle-processing container in the workshop, including the plant owner's wife and son.

Three of them died in hospital, and the others were recuperating, he said.

A preliminary investigation suggested they were poisoned by a leak of sulfureted hydrogen, as the density of the toxic gas measured 668 milligram per cubic meter at the scene, said Wu.

He said investigation was continuing.