Taipei: US House of Representatives Speaker Nancy Pelosi left Taiwan on Wednesday after touting its democracy and pledging American solidarity during her brief visit, adding that Chinese anger cannot stop world leaders from travelling to the self-ruled island claimed by Beijing.

China demonstrated its outrage over the highest-level US visit to the island in 25 years with a burst of military activity in surrounding waters, summoning the US ambassador in Beijing and halting several agricultural imports from Taiwan.

Some of China's planned military exercises were to take place within Taiwan's 12 nautical mile sea and air territory, according to Taiwan's defence ministry, an unprecedented move that a senior defence official described to reporters as "amounting to a sea and air blockade of Taiwan.”

Taiwan scrambled jets on Wednesday to warn away 27 Chinese aircraft in its air defence zone, the island's defence ministry said, adding that 22 of them crossed the median line separating the island from China.

Pelosi arrived with a congressional delegation on her unannounced but closely watched visit late on Tuesday, defying China's repeated warnings, on a trip that she said demonstrated unwavering US commitment to Taiwan's democracy.

"Our delegation came to Taiwan to make unequivocally clear that we will not abandon Taiwan," Pelosi told Taiwan's President Tsai Ing-wen, who Beijing suspects of pushing for formal independence - a red line for China.

"Now, more than ever, America's solidarity with Taiwan is crucial, and that's the message we are bringing here today," Pelosi said during her roughly 19-hour visit.

A long-time China critic, especially on human rights, and a political ally of US President Joe Biden, Pelosi met with a former Tiananmen activist, a Hong Kong bookseller who had been detained by China and a Taiwanese activist recently released by China.

The last US House speaker to go to Taiwan was Newt Gingrich in 1997. Pelosi's visit comes amid sharply deteriorating US-Chinese relations. During the past quarter century, China has become a far more powerful economic, military and geopolitical force.

China considers Taiwan part of its territory and has never renounced using force to bring it under its control. The United States and the foreign ministers of the Group of Seven nations warned China against using the visit as a pretext for military action against Taiwan.

"Sadly, Taiwan has been prevented from participating in global meetings, most recently the World Health Organization, because of objections by the Chinese Communist Party," Pelosi said in statement issued after her departure.

"While they may prevent Taiwan from sending its leaders to global forums, they cannot prevent world leaders or anyone from travelling to Taiwan to pay respect to its flourishing democracy, to highlight its many successes and to reaffirm our commitment to continued collaboration," Pelosi added.

She later arrived in South Korea, according to local media.

China's customs department announced a suspension of imports of citrus fruits and certain fish - chilled white striped hairtail and frozen horse mackerel - from Taiwan, while its commerce ministry banned export of natural sand to Taiwan.

Fury on the mainland over Pelosi's defiance of Beijing was evident in Chinese social media, with one blogger railing: "this old she-devil, she actually dares to come!" Pelosi is 82.

Military drills

China's military announced joint air and sea drills near Taiwan and test launches of conventional missiles in the sea east of the island, with Chinese state news agency Xinhua describing live-fire drills and other exercises around Taiwan from Thursday to Sunday.

China's foreign ministry said Pelosi's visit damages peace and stability in the Taiwan Strait, harms the political foundation of US-Chinese relations and infringes upon China's sovereignty and territorial integrity.

US Secretary of State Antony Blinken discussed the potential for Pelosi's visit with counterpart Wang Yi during a G20 meeting in Bali last month, and said any such trip would be entirely Pelosi's decision and independent of the Biden administration, a senior US official said on Wednesday.

The State Department confirmed that China delivered a formal protest to US Ambassador Nicholas Burns in Beijing, and that Burns reiterated US readiness to work with China to prevent escalation and keep lines of communication open.

The United States has no official diplomatic relations with Taiwan but is bound by American law to provide it with the means to defend itself. China views visits by US officials to Taiwan as sending an encouraging signal to the pro-independence camp on the island. Taiwan rejects China's sovereignty claims, saying only the Taiwanese people can decide the island's future.

Taiwan's military increased its alertness level. Its defence ministry said China was attempting to threaten key ports and cities with drills in the surrounding waters.

"We can see China's ambition: to make the Taiwan Strait non-international waters, as well as making the entire area west of the first island chain in the western pacific its sphere of influence," a senior Taiwan official familiar with its security planning told Reuters.

Foreign ministers of the G7 - Canada, France, Germany, Italy, Japan, Britain and the United States, as well as the European Union – in a statement urged China to resolve the Taiwan matter peacefully and expressed concern over China's "threatening actions," particularly live-fire exercises and "economic coercion." They added that it is "normal and routine" for legislators to travel internationally.