Japan is to deploy upgraded “ship killer” missiles as early as next year, in a move that could offer a lifeline to Taiwan in the event of a Chinese blockade.

Details of the upgraded Type-12 surface-to-ship missile were unveiled in the Japanese defence ministry’s annual white paper last month, alongside a pledge by Minoru Kihara, the defence minister, to urgently enhance the country’s ability to protect itself.

“Japan finds itself in the most severe and complex security environment of the post-war era,” he said in the paper, citing China’s rapid military build-up and joint drills with Russia, and the nuclear weapons threat from North Korea.

“Japan is going to acquire various types of stand-off missiles earlier than originally planned, including Tomahawk missiles and the ground-launched version of upgraded Type-12 surface-to-ship missiles,” he continued.

The paper published an image of the SSM prototype, which has a low-observable nose and foldable swept-back wings. It said the Type-12 would be ready 12 months ahead of schedule.

The new range of the missile has not been officially disclosed, but the Japanese media has reported it would be able to hit targets as far away as 560 miles, with the aim to extend this to 750 to 930 miles.

Naval News reported the shape of the missile had been modified to reduce the radar cross-section and make it stealthy.

If the new ranges are confirmed, the deployment of the missile system in Japan’s south-western islands would put northern Taiwan or its waters within range, said Dr Collin Koh, a senior fellow at the S Rajaratnam School of International Studies in Singapore.

This could prevent China from performing a full blockade of the democratic island and would “open one survival line for Taiwan at least”, he said.

Secondly, the missile deployment could help “constrain the freedom of movement of the PLA [People’s Liberation Army] Navy through the first island chain, especially [its] ability to break out into the open Pacific Ocean,” he said.

The first island chain is a line of archipelagos from Russia’s Kuril Islands to the Malay Peninsula, which acts as a natural barrier to China’s Pacific expansion ambitions.

Alessio Patalano, a professor of war and strategy in East Asia at King’s College London, said the missile was a “much needed conventional capability that can help tilt the scales of the military balance in the air domain back to a situation in which an opposing force is held at serious risk”.

It was “significant” as it would bring back “contestation in the skies above the maritime theatres of East Asia” as a problem Chinese forces would have to contend with, he said.

“Capabilities like this don’t deter on their own terms. They raise tactical costs for aggressive behaviour – but that idea has to be leveraged to create a cognitive political understanding of the costs unfolding from those risks,” he said.

Dr Sidharth Kaushal, a senior research fellow at the Royal United Services Institute, said the missile would allow Japan to “increasingly be able to strike targets such as the transporter erector launchers, which carry missiles inland, as well as being able to engage vessels at sea.”

It could also be launched from a variety of platforms including naval vessels, which would “impose more operational uncertainty than ground-based systems”, he added.

“The ability to strike targets both at sea and on land will both raise the risks of a Chinese clash with Japan in the East China Sea but will also mean the PLA will have to allocate resources to defending against the potential threat that these missiles might pose in the event of a crisis in the Taiwan Strait,” he said.