HARBIN -- Daqing Oilfield, the largest oilfield explored by China's major oil and gas producer PetroChina, is expected to reduce its production starting in 2015.

According to the economic working conference of Northeast China's Heilongjiang province on Saturday, Daqing Oilfield, which produces nearly one-fourth of China's total oil output annually, will see output reduction by 1.5 million tons next year.

By 2020, Daqing's annual output will be slashed to 32 million tons with an annual reduction of more than 1.3 million tons, the conference said.

As China's largest inland oilfield, Daqing has produced more than 2.1 billion tons of crude oil since production started in 1960.

It produced slightly more than 40 million tons of crude oil in 2013, marking the 11th consecutive year in which the crude oil output of Daqing exceeded 40 million tons.

Limited oil reserves, high cost of development and declining international oil prices have caused the fast-depleting Daqing Oilfield to reduce output, a staff who declined to be named from Daqing told Xinhua.

He said the proper adjustment of output can allow the oilfield to develop sustainably and give more time to research on new technologies.

But the output target reduction may put pressure on Heilongjiang's economic growth. The preliminary estimate showed that GDP and fiscal revenue of the province will decrease by more than 20 billion yuan ($3.2 billion) and about six billion yuan respectively in 2015.

In order to offset adverse impact of the output reduction on local economy, the province planned to accelerate its economic restructuring and deepen cooperation with PetroChina by promoting the oil refining projects.