China nuclear sub sank in its dock, US officials say

A Chinese nuclear-powered attack submarine sank in its dock earlier this year while under construction, in a major setback for the Chinese military, according to US defence officials.

Speaking on condition of anonymity to the BBC's US partner, CBS, the officials said the loss of the submarine probably happened between May and June.

Satellite images taken in June show what appear to be floating salvage cranes at the berth in Wuhan where, a month previously, the vessel had been seen. Beijing has not confirmed the reports.

The US officials said it was "not surprising" the Chinese military would have covered up the loss of one of its newest assets.

It is unclear whether the submarine was carrying nuclear fuel at the time.

A Chinese Foreign Ministry spokesperson said on Friday he was not familiar with the topic and did not provide any information when asked about it at a Beijing news conference.

The incident raises questions about China's defence industry, which is allegedly riddled with corruption.

China has the biggest navy in the world, with more than 370 ships, and is currently producing a new generation of nuclear-armed submarines, the Zhou-class, of which this was the first.

Taiwan has said it carried out its own investigations into the fate of the submarine and had "a grasp of the situation through multiple intelligence and surveillance methods", but gave no further details.

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 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.