Admiral Michael Gilday, chief of US naval operations, is the latest senior official in Washington to raise concerns that China's President Xi Jinping may be much more willing than previously thought to seize Taiwan.

Xi is on the cusp of securing a third five-year term at the helm of the world's most populous nation, delivering a landmark Communist Party Congress speech on Sunday where he restated his vow to one day "reunify," or forcefully take, Taiwan.

In a discussion with a think-tank, Gilday was asked about Xi's speech and whether he agreed with comments by another US admiral that Beijing would be ready to take Taiwan by 2027.

"It's not just what President Xi says, it's how the Chinese behave and what they do," Gilday told the Atlantic Council.

"And what we've seen over the past 20 years is that they have delivered on every promise they've made earlier than they said they were going to deliver on it."

"So when we talk about the 2027 window in my mind, that has to be a 2022 window or potentially a 2023 window," he added.

"I can't rule that out. I don't mean at all to be alarmist by saying that. It's just that we can't wish that away."

China's Communist Party has never controlled Taiwan but it claims the self-ruled island as its own.

Taiwan is not a treaty ally of the United States, but Congress is bound by law to sell Taipei defensive weapons and there is bipartisan support for protecting what has become a progressive democracy and vital global trade partner.

Beijing's stance has long been that it seeks "peaceful reunification" with Taiwan but reserves the right to use force if necessary, especially if the island formally declares independence.

The rhetoric and actions towards Taiwan have become more pronounced under Xi, China's most assertive leader in a generation, and the military has ramped up equipment purchases aimed at pulling off an invasion.

Xi has tied taking Taiwan to his vision of the "great rejuvenation of the Chinese nation" and said the goal of reunification cannot continue to be passed indefinitely from generation to generation.

Russia's recent invasion of Ukraine, which China has not condemned, has also raised fears that Beijing might take similar moves against Taiwan's 23 million people.

Gilday's comments came a day after US Secretary of State Anthony Blinken warned that Beijing wants to seize Taiwan "on a much faster timeline" than previously considered, adding that "a very different China" had emerged under Xi.

"It is more repressive at home; it's more aggressive abroad," Blinken said.