China will turn Taiwan into a major nuclear and conventional military base, a move which will allow it to project power into the Indian Ocean and consolidate more control over the disputed South China Sea to "isolate" both India and Japan, a US lawmaker has warned.

Expressing concern over China's growing economic and military power, Richard D Fisher of the International Assessment and Strategy Center told lawmakers yesterday that Beijing had a new strategy for gaining eventual global military access called "debt trap diplomacy".

"China may be using debt pressure right now to force Djibouti to limit US military access in that strategic base. It recently gained ownership of a new large port in Sri Lanka by debt default. Vanuatu, Pakistan, Thailand and others are vulnerable," Fisher said.

A good reason to deter a Chinese invasion of Taiwan, which could be perhaps as early as the mid-2020s, was that China will turn Taiwan into a major nuclear and conventional military base, he said.

"This will then trigger Chinese moves to isolate Japan, consolidate control over the South China Sea even more, project power into the Indian Ocean to isolate India. In Latin America, China will continue to exploit opportunities to cause trouble and gain military access," he said.

China claims almost all of South China Sea and also laid claims on the Senkaku islands under the control of Japan in East China Sea and resorted to aggressive patrols in the last two years.

Vietnam, the Philippines, Malaysia, Brunei and Taiwan have counter claims over the waterway.

The US periodically deploys its naval ships and fighter planes to assert freedom of navigation.

By the 2030s, the Chinese Air Force air mobile projection could be based on 100 to 200 large C-17 size Xian Y-20 heavy transports, and both their lightweight airborne forces and now medium-weight airborne projection forces are anticipated.

China is assembling a power-projection Navy that, by the 2030s, may have the world's first totally nuclear-powered carrier battle group, Fisher said.

It will have an initial amphibious projection of about 12 large ships by probably as early as the early 2030s. And the Chinese marines are reforming into a force of about 100,000.

Other lawmakers also echoed Fisher's concerns over China.

Congressman Devin Nunes, Chairman House Intelligence Committee said during a Congressional hearing, that previous attempts to appease China had failed to improve the bilateral relations.

"In fact, China has only become emboldened and may now be the preeminent threat to American security, our economy and our values," Nunes said.

"From its One Belt Road initiative to its unlawful maritime claims in the South China Sea, China is using its economic and military power to subvert international norms, undermine US national security, threaten our friends and allies, and reshape the global balance of power," Nunes said.

Ranking Member Congressman Adam Schiff said China's military growth had taken place alongside the Belt and Road initiative.

China's massive Belt and Road Initiative (BRI) seeks to build rail, maritime and road links from Asia to Europe and Africa in a revival of ancient Silk Road trading routes.

"Through the BRI and other tools such as the Asian Infrastructure Bank, China seems to be leading in economic engagement and then backfilling with greater military capacity as its capabilities grow," Schiff said.

The Chinese Army base in Djibouti follows decades of Chinese investment in diplomacy in Africa and increasing oil imports by China, much of which passes through the Bab-el-Mandeb strait between Djibouti and Yemen, he said.

"Similarly, Beijing's militarisation of the South China Sea reflects a deliberate approach that seeks to protect core Chinese economic and strategic interests that have long predated the island reclamation effort and the buildup there," he said.

Dan Blumenthal from the American Enterprise Institute said under the BRI initiative, a lot of the major construction and investment projects were going to places like Pakistan and Bangladesh, which will provide outlets for China into the Indian Ocean that don't have to go through the Straits of Malacca and other areas that the US dominate.

"It really is a cash or investment-for-access deal, in many of these places," he said.

"The BRI will never achieve, in my view, what Xi Jinping has said, which is to establish a Silk Road. But, through targeted investments, China will gain a lot in terms of access...The base in Djibouti is a very big deal, a very, very big deal, and is the fruit of cash for diplomacy, as well," he said.