South Korea and China made overlapping claims to an extended portion of continental shelf beyond their exclusive economic zones (EEZs) in the East China Sea, with Seoul set to submit its official claim to a United Nations body this week, officials and experts said Sunday.

Beijing presented its official document to the U.N. Commission on the Limits of the Continental Shelf (CLCS) on Dec. 14, claiming that its natural prolongation of the continental shelf in the sea extends to the Okinawa Trough, according to local media reports.

Its demarcation is extended north-eastward toward South Korea compared to its 2009 preliminary document, experts said.

“In 2009, the Chinese version was located in much southern areas than the recent one,” said an expert on the issue. “The extension toward South Korea seems to guard against its neighbor.”

In its formal report on its continental shelf set to be submitted to the U.N. CLCS later this week, Seoul will also extend its demarcation south-eastward than its previous version, which will widen the overlapping part claimed by the two countries, according to foreign ministry sources here.

South Korea and China have reportedly shared a largely similar stance on the issue, while being at odds with Japan, but the overlapping claims this time could heighten tension, said observers.

The U.N. convention stipulates that, if the continental shelf of a coastal state extends beyond 200 nautical miles from the baselines from which the width of the territorial sea is measured, the relevant information on its limits of the shelf shall be submitted by the country to the U.N. CLCS. In the EEZ, a country is eligible for exclusive rights to the exploration and use of marine resources.

The continental shelf in the East China Sea is believed to contain rich natural gas and oil deposits. (Yonhap News)