Washington: China's newest nuclear-powered submarine sank pier-side in the spring, and the Chinese navy tried to conceal details regarding the loss, CNN reported, citing two US defence officials.

The official said that the attack submarine was the first of its new Zhou-class line of vessels, under construction at a shipyard near Wuhan. The Zhou-class submarines have a distinctive X-shaped stern, made to improve manoeuvrability underwater.

A satellite image from March 10, captured by Maxar Technologies, shows the Zhou-class sub, with its signature x-shape tail, docked at the port. Furthermore, Maxar imagery reviewed in June shows that the sub did not return to the pier, according to CNN.

The senior US defence official said, "It's not surprising that the PLA Navy would try to conceal the fact that their new first-in-class nuclear-powered attack submarine sank pier-side."

Tom Shugart, an adjunct senior fellow at the Centre for a New American Security who routinely studies satellite imagery of Chinese shipyards, was the first one who observed the unusual activity at the shipyard.

"I've never seen a bunch of cranes clustered around (one spot)," Shugart said. "If you go back and look at historical imagery, you can see one crane, but not a bunch clustered there."

Looking at older satellite images of the same shipyard, Shugart noticed the submarine's larger size and its distinctive tail, reflecting a new class of submarine.

"Usually, those submarines, after they get launched, they're there at the shipyard for several months in outfitting. And it wasn't there anymore," he stated.

Notably, China has made modernisation of the People's Liberation Army (PLA) Navy and its submarine force one of its top priorities as it tries to build a world-class military on par with the US. The PLA Navy operates six nuclear-powered ballistic missile submarines, six nuclear-powered attack submarines, and 48 diesel-powered attack submarines, as per the China military report from 2023.

The US Navy has 14 ballistic missile submarines, four guided-missile submarines, 53 fast attack submarines, and the entire US submarine fleet is nuclear-powered.

The Wall Street Journal first reported about the Chinese submarine's sinking. The senior defence official said it is not clear whether nuclear fuel had already been loaded onto the submarine or if the vessel was unfuelled when it sank.

A spokesperson from the Chinese Embassy in Washington, DC, said: "We are not familiar with the situation you mentioned and currently have no information to provide," according to CNN report.

China is working on bolstering its ability to make new submarines. Even after the older submarines retire from the PLA Navy, China is expected to have 65 submarines in 2025 and 80 in 2035 due to the growth in its submarine construction capacity, CNN reported, citing the Congressional Research Service (CRS).

In terms of the number of ships, China has the world's largest navy. The PLA Navy has 370 platforms, which comprise 234 warships, according to CRS. Meanwhile, the US has 219 warships.

Speaking about the Chinese industrial base, the defence official stressed that the incident raises "deeper questions about PLA's internal accountability and oversight of China's defence industry--which has long been plagued by corruption."

(With Inputs From Agencies)