A Chinese naval ship has been spotted at sea equipped with an experimental railgun that US intelligence analysts reportedly believe could fire projectiles at seven times the speed of sound.

An enormous gun turret mounted to the bow of what Australian media said was the landing ship Haiyang Shan is seen in a murky photo posted to Weibo, China’s hugely popular social network.

The vessel was the centre of speculation last year after images emerged of her in port at about the same time as several state media reports talked up China’s advancements in electromagnetic weaponry.

The non-standard turret was in place at that time, along with additional structures on the deck.

The new image suggests Beijing may have beaten the US to the punch in mounting a railgun on a ship for trials at sea. While the original source of the file is not clear, ABC News reported it was taken by a defence blogger.

A report by Hong Kong-based Asia Times last spring claimed sea trials were already under way.

Railguns generate an electromagnetic charge to expel projectiles at velocities much faster than conventional gunpowder can achieve.

US intelligence services believe rounds fired by China’s version of the experimental cannon can reach 1.6 miles per second – some 5,700mph, or above Mach 7 – according to a CNBC News report from last June. Analysts believe it could be operation by 2025, the site reported.

Their extraordinary speed would make the shells, designed to cause damage through sheer kinetic force, difficult to destroy in flight or evade. This is also the rationale behind the development of hypersonic cruise missiles, which could pose a serious threat to enemy ships.

Another benefit of railguns would be an end to the requirement of storing dangerous explosive ammunition and propellant aboard ships. However, the weapons require huge electric power plants to function, which has proved a technological hurdle in their development.

Global Times, China’s state-run tabloid, was quick to capitalise on international media coverage of the Weibo image, citing a naval expert as saying the railgun system had “reached a mature stage after a series of tests” in a report published on Thursday.

The site has previously lauded the People’s Liberation Army Navy’s “notable achievements” in testing the weapon, and claimed that scientists had developed a “repeating power supply system” to power it.

The US also has a railgun system in development, as well as hypersonic missiles and a hypersonic projectile that is designed to be fired from existing guns.

Railgun development is one aspect of China’s recent military evolution. It has developed its own fighter jet and launched a domestically-built aircraft carrier while building up artificial islands and bases far offshore, to the consternation of its neighbours.

The US and UK have both sailed warships through the South China Sea to assert freedom of navigation rights, which Beijing has called “provocative”. The Permanent Court of Arbitration in The Hague has ruled there is no legal basis for China’s maritime claims over waters hundreds of miles beyond its shores.

The Global Times said Beijing planned to mount its eventual railgun system to another domestically-produced warship, the Type 055 guided missile destroyer.

Reports of the railgun sighting came as China demonstrated its technological prowess by landing a probe on the far side of the moon, a first for humanity.