PetroChina has switched off the natural gas supply to fertilizer producer Cangzhou Dahua Co Ltd , the company said in a statement on Wednesday, another sign of the country's shortage of the fuel heading into winter.

Chinese energy firms are moving to free up gas for residential and transportation use.

Cangzhou Dahua, based in Hebei province neighboring the capital city Beijing, said the cut-off of gas would lead to a production halt. It didn't say how long the gas would be suspended.

China's top oil and gas firms - PetroChina, Sinopec Corp and CNOOC Ltd - have all pledged to boost gas supplies in the coming months either by maximizing domestic production or raising imports.

Sinopec said last week it would free up gas supplies over winter partly by cutting deliveries to its vinylon plant in the southwestern province of Sichuan.