China has been planning to build the world's longest undersea railway tunnel that would link the mainland and Taiwan, with scientists close to confirming its design.

At 135 kilometres (84 miles), the proposed Taiwan Strait Tunnel would be more than three times the length of the Channel Tunnel between Britain and France, which is currently the world's longest undersea rail tunnel.

The billion-pound project aims to take high-speed trains through the Taiwan Strait at up to 250km/h (155mph) by 2030, according to South China Morning Post.

However, despite the latest technological progress, political tensions between Taiwan and Beijing - which regards the self-ruled island as a part of its territory - mean construction is unlikely to start any time soon, the report said.

A Fuxing bullet train runs on the Beijing-Shanghai High-Speed Railway. China has been planning to build an undersea railway tunnel that would link the mainland and Taiwan

Pingtan Island is physically China's closest spot to Taiwan and is the chosen starting point of the multi-billion-yuan project. The idea of building the tunnel was first proposed in 1996

The idea of building a tunnel under the Taiwan Strait has been around since 1996, when it was first proposed by Tsinghua University professor Wu Zhiming following a visit to the Channel Tunnel, which is 37.9km (23.5 miles) long.

The ambitious project achieved new prominence in 2016, when Beijing included a cross-strait high-speed rail network in its then-new five-year plan.

According to the plan, the train will travel from Fuzhou province's Pingtan county and arrive in Hsinchu city, south-west of Taipei in 32 minutes. The regions lie on the opposite sides of the Taiwan Strait.

The tunnel's design, completed last year with funding from the Chinese Academy of Engineering, has the growing support of both China’s research community and tunnelling industry, several senior civil engineering experts told South China Morning Post.

The idea of building a tunnel under the Taiwan Strait was inspired by the Channel Tunnel

The train would travel from Fuzhou province's Pingtan county and arrive in Hsinchu city, south-west of Taipei in 32 minutes. The regions lie on the opposite sides of the Taiwan Strait

Some researchers reportedly said it was possible that Beijing would start to work on the project in a unilateral, and largely symbolic move.

The railway's layout consists of a complex of three individual tunnels. Two main passages would be used by trains running in opposite directions. In between them would be a smaller service tunnel that would contain power lines, communication cables and emergency exits, according to the report.

The breadth of its main tunnels would be nearly a third larger than those of the Channel Tunnel, allowing trains to travel faster and carry bulkier cargos. Trains are restricted to operate at a speed of 160km/h (99mph) in the Channel Tunnel.

The particular sea area in the Taiwan Strait, with a comparatively stable geological structure and shallower water, is not situated in the region prone to strong earthquakes, thus making it suitable for tunnel construction, according to a previous report by China Daily.

The shuttle train will return to the surface in Hsinchu (pictured), a coastal city near Taipei

At the same time, a 12-billion-yuan (£1.3 billion) 'warm-up' project - the Pingtan-Fuqing passageway in Fuzhou - is currently under assessment. Once realised, the road tunnel could reportedly 'pave the way' for the official launch of the mega cross-strait construction.

The shorter tunnel, running more than 11 kilometres (6.8 miles) under the seabed, would be located in roughly the same area as the rail tunnel, according to the report.

According to SCMP, a research team has been at work off the coast of Pingtan conducting geological mapping, drilling for rock samples, running computer simulations and analysing the potential environmental risks and impact of a large-scale tunnelling project.

More than six decades after Taiwan's split from China, Beijing has remained adamant to unify Taiwan with the mainland, stepping up diplomatic and military pressure on the self-governing neighbour under the 'One China policy'.

However, under the rule of pro-independence President Tsai Ing-wen, Taiwan still sees itself as a sovereign country, prompting experts to say that the strait tunnel is likely to remain as a 'one-sided move' from Beijing.