China established a regular patrol system in the East China Sea last year, an official report said.

The annual report, reviewing the State Oceanographic Bureau's administrative enforcement of the law in the past year, said the bureau had sent ocean surveillance ships and airplanes on patrols in the East China Sea.

The vessels and planes watched and turned back foreign vessels that were not authorized to explore for oil and gas in the continental shelf of the East China Sea, and those that disrupted China's natural gas exploration activities inside its offshore area instead of the disputed area.

The monitoring team also ordered several military surveillance ships from the United States to stop unauthorized ocean surveys in the sea area last year.

"The regular patrol system in the East China Sea demonstrates the Chinese government's determination and capacity to administer the East China Sea. It also safeguards China's maritime rights," said the report, which was signed by Sun Zhihui, the bureau director

The East China Sea covers an area of more than 700,000 square kilometers, with the east side reaching Japan. The average water depth is 350 meters.

It is estimated that about 7.2 billion tons of gas and oil resources are buried in the East China Sea.

The sea is abundant with scarce metals such as cobalt, manganese and nickel, which can be used to manufacture aerospace equipment and precision machine tools.

In addition to the regular patrol system, the bureau strengthened inspections of sea use last year and carried out more than 45,000 checks, the report said.

The bureau has cracked down on 3,100 illegal activities, and issued fines of 107 million yuan ($13.8 million).

More than 80 percent of the illegal sea use cases were projects reclaiming land from the sea and fishing.

The bureau has inspected more than 1,000 projects reclaiming land from the sea, and a third of them involved illegal operations.

Other illegal cases included changing the function of a sea area without government approval and not paying due fees for sea use.