China's ocean watchdog said the country's dynamic sea-monitoring system now covers the Diaoyu Islands, the Xisha Islands and Huangyan Island.

After three years of operation, the national dynamic sea-monitoring system has gradually expanded its coverage from offshore areas to distant waters, covering about 300,000 square km, according to the State Oceanic Administration.

Through satellite images and aerial remote sensing, the system is able to supervise illegal use of seawater, the administration said.

For important maritime projects, the system will receive satellite monitoring pictures every one or two months to keep close watch on the progress.

Combined with the China Marine Surveillance examination, the data will provide information to policymakers in seawater management and the annual national sea-use plan.

In 2011, 1,433 cases involving illegal seawater use were detected in the offshore and distant-water areas, and another 601 cases involved sea pollution, according to an annual report on the country's marine environment.