China outlined plans to build a modern, high-tech army. (File image)

China outlined plans to build a modern, high-tech army in a national defence plan published Wednesday, while accusing Washington of undermining global strategic stability and warning against Taiwanese independence.

The first white paper since 2012 gives rare insight into the world's largest army and Beijing's military ambitions.

"International strategic competition is on the rise," the document says, adding that the United States has adjusted its national security and defence strategies and adopted "unilateral policies".

The US "has provoked and intensified competition among major countries, significantly increased its defence expenditure, pushed for additional capacity in nuclear, outer space, cyber and missile defence, and undermined global strategic stability".

The plan calls for more cutting-edge technology in the People's Liberation Army (PLA) arsenal, admitting it "still lags far behind the world's leading militaries".

War is evolving towards "intelligent warfare", the national security plan says, citing a growing use of AI, big data, cloud computing and "new and high-tech military technologies based on IT".

China's defence spending is second only to the United States, and it said earlier this year it planned to increase it by 7.5 percent in 2019.

Despite the ambitious plans, it insists the Chinese army is a "staunch force for world peace".

But within its own borders it is less sanguine, promising to "crack down" on separatists in Xinjiang and Tibet.

Beijing is firmer still on the self-ruled island of Taiwan -- which China views as its own territory -- and makes "no promise to renounce the use of force" in bringing it back into the fold.

"China must be and will be reunited," the paper reads. "China has the firm resolve and the ability to safeguard national sovereignty... and will never allow the secession of any part of its territory by anyone."

It says Taiwan "separatists" are the biggest threat to the peaceful reunification of the country.

"The PLA will resolutely defeat anyone attempting to separate Taiwan from China," is says.

The PLA has been focused on catching up with technology used by armed forces in the US and western Europe, and is reportedly building a third aircraft carrier as well as developing new generation destroyer vessels, fighter jets and ballistic missiles.