China's new nuclear submarine sinks during construction, says US official

Satellite imagery appears to show China's new nuclear-powered submarine sinking at a shipyard while under construction, a senior US defence official has said.

The sinking of China's first Zhou-class submarine represents a setback for Beijing as it seeks to increase the size of what is already the world's largest navy.

It comes as Beijing has become increasingly assertive in its claims over the South China Sea, which is crucial to international trade.

The Chinese Embassy in Washington on Thursday said it was "not familiar with the situation" in relation to the submarine and it did not have information to provide.

The vessel likely sank between May and June, when satellite images showed cranes that would be necessary to lift it off the bottom of the river, said the US official, who spoke on the condition of anonymity to provide details about the incident.

They added it was not clear what caused it to sink or whether it had nuclear fuel on board at the time.

There has been no reported release of radiation in the area in the time since.

"In addition to the obvious questions about training standards and equipment quality, the incident raises deeper questions about the PLA's internal accountability and oversight of China's defence industry," the official said.

The People's Liberation Army (PLA) is the armed wing of the Chinese Communist Party.

What do the satellite images show?

The satellite images from Planet Labs PBC show what appears to be a submarine docked at the Shuangliu shipyard on the Yangtze River, near Wuhan, before the incident.

An image taken on 15 June appears to show the submarine either fully or partially submerged just under the river's surface, with rescue equipment and cranes surrounding it.

Booms surround it to prevent any oil or other leaks from the vessel.

A satellite image taken on 25 August shows a submarine back at the same dock as the submerged vessel. It's not clear if it was the same one.

South China Sea tensions

China has been engaged in a long-time dispute with Brunei, Malaysia, the Philippines, Taiwan and Vietnam in relation to the South China Sea - as all the countries have competing territorial claims over the waters.

The United States has sought to strengthen ties with its allies in the region and regularly sails through those waters in operations it says maintains the freedom of navigation for vessels there - angering Beijing.

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China already has the largest navy in the world, with more than 370 ships, and it has embarked on production of a new generation of nuclear-armed submarines.

The US considers China's rise one of its main future security concerns.

The senior US defence official said it was "not surprising" China's navy would conceal the sinking of the submarine.

The vessel's current status is unknown.

It's sinking was first reported by The Wall Street Journal.