China's armed forces must strengthen their sense of urgency and do everything they can to prepare for battle, President Xi Jinping told a meeting of top brass on Friday.

Key points: China is facing several challenges, including the US trade war and territorial disputes over the South China Sea and Taiwan

China is facing several challenges, including the US trade war and territorial disputes over the South China Sea and Taiwan Xi Jinping wants the country's military to "nurture new types of combat forces"

Xi Jinping wants the country's military to "nurture new types of combat forces" The US recently signed an agreement in support of Taiwan's security

China is keen to beef up its armed forces amid territorial disputes in the South China Sea amid escalating tension with the United States over issues ranging from trade to the status of Taiwan.

The official Xinhua news agency reported that Mr Xi told a meeting of the top military authority that China faced increasing risks and challenges and that armed forces must work to secure its security and development needs.

Mr Xi, who is also chairman of the Central Military Commission, said the armed forces must devise strategies for the new era and take on responsibilities for preparing and waging war.

"The world is facing a period of major changes never seen in a century, and China is still in an important period of strategic opportunity for development," he was quoted as saying.

He said the armed forces needed to be able to respond quickly to emergencies, needed to upgrade their joint operations capabilities and nurture new types of combat forces.

The speech was made just days after US President Donald Trump signed the Asia Reassurance Initiative Act into law, reaffirming the US's commitment to the island's security.

Mr Xi's comments followed his remarks on Wednesday that nobody could change the fact that Taiwan was part of China, and that people on both sides of the Taiwan Strait should seek "reunification".

He added that China still reserved the right to use force to achieve this "reunification".

Taiwan President Tsai Ing-wen vowed on Saturday to defend the self-ruled island's democracy and way of life.

She said the island would not accept a "one country, two systems" political arrangement with China, while stressing all cross-Strait negotiations needed to be carried out on a government-to-government basis.

The gun on the bow is claimed to be a prototype railgun. ( Haohan-Red Shark via Storyful )

Mr Xi's comments came just days after a Chinese warship was spotted carrying a railgun, which uses a high-powered electric circuit to shoot a projectile along magnetic rails, firing at hypersonic speeds five times the speed of sound.

Experts say the use of ship-mounted railguns could have the potential to usher in a "hemispheric battle space".

"This would see belligerents able to strike at each other at distances ranging in the hundreds of kilometres", Dr Malcolm Davis, a senior analyst at the Australian Strategic Policy Institute, said.

Reuters