PetroChina Co has begun tapping its underground gas reserves to meet higher demand for winter heating in north China.

The company pumped 5.7 million cubic meters of gas from its Dagang storage base on Monday and 8 million cubic meters on Tuesday, according to a statement by its parent, China National Petroleum Corp.

Gas consumption has been rising as winter approaches and many of PetroChina's gas pipelines have been already running at full capacity since last month.

Though regional shortages could occur due to production and delivery constraints, industry officials have said this year's situation could be better than last year's as overall demand could be met by higher imports.

But critics also cited monopoly as a reason for the shortages.

PetroChina, the nation's dominant gas supplier, has forecast that the gas shortage in Beijing, Tianjin and neighboring areas could reach 9 million cubic meters a day this winter.

The Dagang base, China's largest underground gas reserve, holds a record 185 million cubic meters while the newly built Huabei base stores 100 million cubic meters. The two bases help ensure peak winter demand in the northern region.

China also is in talks with Russia, which has massive amounts of natural gas, on a deal to import the fuel.

A National Energy Administration official said last month the government may limit gas supplies at factories to ensure residential use and has told state companies to boost production and imports.

PetroChina has asked the government to speed up price reforms as importers buy at higher international rates and sell at lower regulated prices. To encourage production, China raised wholesale gas prices by 25 percent in June.