The USS Connecticut, a nuclear-powered fast-attack submarine, "struck an object while submerged on the afternoon of Oct. 2, while operating in international waters in the Indo-Pacific region," the navy said in a statement.

It said there were no life-threatening injuries, but USNI News, a site specializing in navy news, reported that about a dozen sailors were hurt "with moderate to minor injuries."

USNI News also said the submarine was operating in the South China Sea, where the US Navy has sought to challenge China's disputed territorial claims on small islands, reefs and outcrops.

Beijing claims almost the entire South China Sea, parts of which are also claimed by four Southeast Asian countries as well as the self-ruled island of Taiwan.

Chinese foreign ministry spokesman Zhao Lijian said Friday that Beijing was "extremely concerned" about the collision and accused the US of deliberately concealing the nature of the incident.

Washington should provide "detailed clarification" of the event, including information about what the submarine collided with, whether it caused nuclear leakage and whether it damaged the local marine environment, Zhao said at a regular press briefing.

He accused the US of long "disturbing the peace" in the South China Sea "under the banner of freedom of navigation."

The US Navy said the extent of the damage is being examined and the incident investigated.

"The submarine remains in a safe and stable condition. USS Connecticut's nuclear propulsion plant and spaces were not affected and remain fully operational," it said.

USNI News said the vessel is now headed to the US base at Guam.