A worker is seen on a production line at a lithium battery manufacturing plant for automotive use in Tangshan, north China's Hebei Province, April 11, 2019. (Xinhua/Yang Shiyao)

Technicians debug firefighting robots just off the production line at a firefighting robot factory in Tangshan, north China's Hebei Province, March 26, 2019. (Xinhua/Yang Shiyao)

A worker is seen on a production line at a lithium battery manufacturing plant for automotive use in Tangshan, north China's Hebei Province, April 11, 2019. (Xinhua/Yang Shiyao)

A worker is seen on the production line of an automobile transmission manufacturer in Fengrun District in Tangshan, north China's Hebei Province, April 12, 2019. (Xinhua/Yang Shiyao)

A worker is seen on a production line at a lithium battery manufacturing plant for automotive use in Tangshan, north China's Hebei Province, April 11, 2019. (Xinhua/Yang Shiyao)

A worker is seen at a lithium battery manufacturing plant for automotive use in Tangshan, north China's Hebei Province, April 11, 2019. (Xinhua/Yang Shiyao)