Beijing has put its nuclear-powered submarine fleet on public display, with state media Tuesday touting the move as unprecedented and necessary to show other countries China's strike capabilities as territorial tensions mount.

In an overt declaration of China's high-seas strength, several state-run papers ran front-page stories on the four-decade-old submarine fleet, while state broadcaster CCTV has devoted much airtime in recent days to its drills and exercises.

China's first nuclear-powered submarine was launched in 1970, the Global Times said, but had not been properly taken into account by others.

"China is powerful in possessing a credible second-strike nuclear capability," it said in an editorial Tuesday, adding: "Some countries haven't taken this into serious consideration when constituting their China policy, leading to a frivolous attitude toward China in public opinion."

"China needs to make it clear that the only choice is not to challenge China's core interest," said the paper, which often takes a nationalistic tone and is close to the ruling Communist party. "Developing marine-based nuclear power is part of such work."

In a nod to accusations that Beijing is becoming increasingly assertive over its territorial claims in the East and South China Seas, the editorial continued: "Perhaps it will give excuse to 'China Threat' speculation but the benefit will far eclipse the trouble created by external opinions."

The media reports have focused on China's older Xia-class submarines, rather than its newer Jin-class vessels.

But analysts said the footage could be intended as a reminder that the world's second-largest defence spender is growing in confidence and building an even more powerful fleet.

"What they're showing you, they're pretty much just stock scenes," said Richard Bitzinger, senior fellow at the S. Rajaratnam School of International Studies at Singapore's Nanyang Technological University, adding that it might constitute "very subtle sabre-rattling".

"They're kind of reinforcing the fact that China has a nuclear Navy," he said. "And if you want to start inferring things, they're just sort of telling you, 'We have nuclear-powered vessels, and most people know that we're getting newer ones, and these are an integrated part of the fleet.'"

China's display comes as relations with Japan become increasingly fraught, with a bitter dispute over the Tokyo-controlled Senkaku islands, claimed by Beijing as the Diaoyus.

In recent months China has also butted heads with southeast Asian neighbours, including the Philippines, over its claims to strategically important and potentially mineral-rich waters in the South China Sea.

The United States has also declared a so-called "pivot" towards Asia, and announced plans to step up its military presence in the region.

China's first nuclear-powered submarine was recently decommissioned after more than 40 years' service, the first of the vessels to be retired, the People's Liberation Army Daily reported Tuesday.