Chinese President Xi Jinping wants to take advantage of what he believes is the waning influence of the United States around the world under President Donald Trump, said Nicholas Burns, whose 27-year career in diplomacy spanned both Republican and Democratic administrations.

Xi is consolidating power at a "very consequential" meeting of communist officials being held this week in Beijing, Burns told CNBC on Wednesday. The gathering, the Communist Party Congress, is holding its 19th session. The event happens once every five years.

"Xi is just about to become Xi Jinping the most powerful Chinese leader in 45 years since Mao Zedong [founder of the People's Republic of China and former chairman of the Chinese Communist Party]; more powerful than the great Deng Xiaoping who ushered capitalism, not really socialism, into China," said Burns, the U.S. ambassador to NATO and the State Department's third-ranking official during George W. Bush's presidency.

"It's an affirmation of big changes over the past five years," said Burns, currently a professor at the Harvard Kennedy School of Government. "China is pushing out very assertively against its neighbors in the South and East China Sea."