Tensions between China and the United States have soared to their highest level in decades since House Speaker Nancy Pelosi's visit triggered Beijing's unprecedented show of force around the island earlier this month.

Blackburn, a Republican from Tennessee, landed at Taipei's Songshan airport in a small US government plane shortly before midnight for what Taiwan's foreign ministry said was a solo visit.

"I just landed in Taiwan to send a message to Beijing -- we will not be bullied," she tweeted.

"The United States remains steadfast in preserving freedom around the globe, and will not tolerate efforts to undermine our nation and our allies."

In a separate statement, Blackburn said she was looking forward to "meeting with leaders in Taipei to advance and strengthen our partnerships".

Taiwan's ministry of foreign affairs said it was "grateful that US congress people have once again demonstrated their firm support and commitment to Taiwan by visiting" at a time "when China continues to heighten its threat".

Beijing claims the self-ruled democratic island as part of its own territory and has vowed to seize it one day -- by force if necessary.

It lashes out at any diplomatic action that might lend Taiwan legitimacy and has responded with growing anger to visits by Western officials and politicians.

Pelosi, second in line to the US presidency after the vice president, was the highest-ranking elected American official to visit Taiwan in decades.

For a week after her visit, Beijing sent warships, missiles and jets into the waters and skies around the island, the largest military exercises of their kind since the mid-1990s.

Taiwan has accused Beijing of using Pelosi's visit as an excuse to kickstart drills that could serve as a rehearsal for an invasion.

Chinese military figures have spoken publicly about the exercises being a dry run for a possible blockade of Taiwan.

- Soaring tensions -

While the Biden administration was quietly opposed to Pelosi's visit, the United States maintains a separation of powers between its executive and legislative branches, and repeatedly said in public that she had the right to travel.

"Members of Congress and elected officials have gone to Taiwan for decades and will continue to do so and this is in line and is consistent with our longstanding One-China policy," State Department spokesman Vedant Patel told reporters when asked about Blackburn's visit.

Another congressional delegation led by Senator Ed Markey visited Taiwan shortly after Pelosi while China was still holding its military exercises.

Then earlier this week, Indiana's Republican governor Eric Holcomb arrived on the heels of the announcement of trade talks between Washington and Taipei in the coming months.

Blackburn, who sits on the Senate's commerce and armed services committees, is a vocal supporter of former president Donald Trump.

In 2020, she tweeted that "China has a 5,000 year history of cheating and stealing" -- a message that provoked widespread anger within the country.

Beijing has adopted an increasingly bellicose approach to Taiwan under President Xi Jinping, China's most authoritarian leader in a generation.

Relations worsened after the 2016 election of Taiwan's President Tsai Ing-wen, who views the island as a sovereign nation and not a part of China.

Like most nations, the United States officially recognises China over Taiwan but it remains a key ally of Taipei and maintains de facto diplomatic ties with the island.

Washington's official policy opposes both Taiwan declaring independence and China forcibly changing the island's status.