BEIJING - China has started filling the tanks of a strategic oil reserve meant to insulate the country from disruptions in supplies, an official said Friday.

The tanks in Zhenhai, a city in the coastal province of Zhejiang, south of Shanghai, are being filled with domestically produced oil, said Xu Dingming, deputy director of the State Energy Office.

Xu didn't say how much oil had been pumped into the tanks or when the process was to be completed.

"All of the construction work (in Zhenhai) has been completed," Xu told Dow Jones Newswires at an energy conference. "Since the storage facility has been built, it must be put into operation as soon as possible."

The Zhenhai facility, with 16 massive oil tanks, is one of four planned sites for petroleum reserves. The others are to be built next year and in 2008.

Previous reports said Beijing plans to stockpile up to 100 million barrels of petroleum, or the equivalent of almost a month's national consumption.

The United States operates a similar reserve.

China supplied its own oil for decades from domestic oil fields, but became a net importer in the 1990s. Driven by a booming economy, it has quickly risen to become the world's third-biggest oil importer, after Japan and the United States.

Xu's agency was created this year to coordinate energy policy and supervise state-owned oil companies and other resources.