China nuclear sub sank in its dock, US officials say

Thomas Shugart, a former US Navy submariner and an analyst at the Center for a New American Security, first noticed the incident involving the submarine in July.

He told the BBC the sinking was a "setback" that would cause "pretty significant embarrassment" for the People's Liberation Army (PLA) navy, but the safety risk was probably "pretty low".

However, he added: "If this ship eventually does get repaired, and I'm sure it will, it'll be a far more capable submarine than what they were building before at that shipyard.

"I do not see it significantly altering the really impressive upward trajectory of the PLA navy’s capability."

The sinking comes at a time when Beijing has been increasingly assertive in laying claim to virtually the whole South China Sea, which is crucial to international trade.

It has long-standing maritime disputes with other nations in the region, including Brunei, Malaysia, the Philippines, Taiwan and Vietnam.

Read the full story and more from BBC News.