BEIJING–A Vietnam-China standoff over an oil rig exemplifies only a part of the interlocking interests–from the resources under its seabed to the trade routes on its surface–that trouble the waters of the South China Sea.

The sea is believed to contain significant resources, but disputes over its islands, reefs and atolls–control of which gives the holder right to extract hydrocarbons and manage fisheries in the waters around them–have made it hard both to gauge the scope of its riches as well as to exploit them.

China claims the sea nearly in its entirety, seeing it as its historic waters, a source of energy and protein for a rapidly growing country, a lifeline for its commerce and a buffer zone against the U.S. military. The sea is claimed in parts by five other governments.

While its reserves are thought to be small compared with some other energy-producing regions, including North America, they could help China reduce dependence on energy from the Middle East and Africa.

The most recent flare-up in tensions began earlier this month after Vietnam sought to stop China from drilling for oil from a deep-water rig it parked off the Paracel Islands, which China controls but which are also claimed by Hanoi.

Rear Adm. Ngo Ngoc Thu, vice commander of Vietnam’s coast guard, said on Tuesday that China had more than 80 ships around the oil rig, including an antisubmarine ship. China has denied that it has sent military vessels to the site.

At a regular news briefing Tuesday, Chinese Foreign Ministry spokeswoman Hua Chunying said Vietnam had disrupted Chinese companies’ normal operations and that China had to take necessary steps to ensure the security of facilities and personnel.

Ms. Hua also lashed out at comments made by U.S. Secretary of State John Kerry in a phone call with Chinese Foreign Minister Wang Yi on Tuesday in which Mr. Kerry called China’s recent actions “provocative.” Ms. Hua said, “There are countries taking provocation, but it is by no means China.”

Adm. Thu said the Chinese oil rig appears to have begun the oil-drilling process. Officials at the rig’s operator, China National Offshore Oil Corp., or Cnooc, couldn’t be reached for comment.

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