In this photo released by the Taiwan Ministry of Foreign Affairs, U.S. House Speaker Nancy Pelosi, center, walks with Taiwan's Foreign Minister Joseph Wu, left, as she arrives in Taipei, Taiwan, Aug. 2. AP-Yonhap

U.S. House Speaker Nancy Pelosi landed in Taiwan late Tuesday, defying a string of increasingly stark warnings and threats from China that have sent tensions between the world's two superpowers soaring.

Pelosi, second in line to the presidency, is the highest-profile elected U.S. official to visit Taiwan in 25 years and Beijing has made clear that it regards her presence as a major provocation, setting the region on edge.

Live broadcasts showed the 82-year-old lawmaker, who flew on a U.S. military aircraft, being greeted at Taipei's Songshan Airport by foreign minister Joseph Wu.

"Our delegation's visit to Taiwan honors America's unwavering commitment to supporting Taiwan's vibrant democracy," she said in a statement upon her arrival, adding that her visit "in no way contradicts" U.S. policy towards Taipei and Beijing.

Taiwan said the trip displayed "rock solid" support from Washington.

Reaction from Beijing was swift with U.S. Ambassador Nicholas Burns summoned by the Foreign Ministry late Tuesday and warned that Washington "shall pay the price" for Pelosi's visit.

"The move is extremely egregious in nature and the consequences are extremely serious," China's Vice Foreign Minister Xie Feng was quoted as saying by the state news agency Xinhua. "China will not sit idly by."

Pelosi is currently on a tour of Asia and while neither she nor her office confirmed the Taipei visit in advance, multiple U.S. and Taiwanese media outlets reported it was on the cards ― triggering days of mounting anger from Beijing.

China's military said it was on "high alert" and would "launch a series of targeted military actions in response" to the visit.

It promptly announced plans for a series of military exercises in waters around the island to begin on Wednesday, including "long-range live ammunition shooting" in the Taiwan Strait.

"Those who play with fire will perish by it," Beijing's foreign ministry added.

Taiwan's defence ministry said more than 21 Chinese military aircraft had flown on Tuesday into Taiwan's air defence identification zone ― an area wider than its territorial airspace that overlaps with part of China's own air defence zone.

No need for 'crisis'

China considers self-ruled, democratic Taiwan as its territory and has vowed to one day seize the island, by force if necessary.

It tries to keep Taiwan isolated on the world stage and opposes countries having official exchanges with Taipei.