WASHINGTON (AFP) — The United States military must be ready to respond to a potential invasion of Taiwan as soon as this year, a senior admiral has said, signaling heightened alarm over Beijing's intentions towards the island.

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.

His comments came Wednesday as Taiwan's top security official warned any attempt to invade the island would fail and turn China into an international pariah.

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."

Military analysts have long warned that even with strength in numbers invading Taiwan is a difficult task, given its location and terrain.

Taiwan's national security chief Chen Ming-tong echoed that sentiment and delivered his own warning to Xi.