US media outlets have reported that China's newest nuclear-powered submarine sank while under construction, citing a US official.

On Thursday, the Associated Press and other media quoted a senior US defense official as saying that satellite imagery showed the submarine sank at a shipyard on the Yangtze River in Hubei Province sometime between May and June.

The reports did not say what caused the submarine to sink.

A senior US government official told NHK that Washington can confirm that the submarine sank. But the official said whether it was carrying nuclear fuel at that time is unclear.

Chinese authorities have not disclosed any relevant information.

The US defense official reportedly told the media that it is not surprising that China would try to conceal the sinking.

China is rushing to bolster its naval power. The official was quoted as saying that the alleged incident is "a major setback to one of the country's priority weapons programs."