(Reuters) - U.S. House of Representatives Speaker Nancy Pelosi left Taiwan on Wednesday after pledging solidarity and hailing its democracy, leaving a trail of Chinese anger over her brief visit to the self-ruled island that Beijing claims as its own.

China demonstrated its outrage over the highest-level U.S. visit to the island in 25 years with a burst of military activity in surrounding waters, summoning the U.S. 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 a senior defence official described to reporters as "amounting to a sea and air blockade of Taiwan".

Pelosi arrived with a congressional delegation on her unannounced but closely watched visit late on Tuesday, defying China's repeated warnings, in what she said shows unwavering U.S. commitment to Taiwan's democracy.

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

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

A long-time China critic, especially on human rights, 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.

Fury on the mainland over the 82-year-old Democrat's defiance of Beijing was evident all over Chinese social media, with one blogger railing: "this old she-devil, she actually dares to come!" read more

The last U.S. house speaker to go to Taiwan was Newt Gingrich, in 1997. But Pelosi's visit comes amid sharply deteriorating Sino-U.S. relations, and during the past quarter century China has emerged as 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 warned China against using the visit as a pretext for military action against Taiwan.

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

While there was little sign of protest against U.S. targets or consumer goods, there was a significant police presence outside the U.S. consulate in Shanghai and what appeared to be more security than usual outside the embassy in Beijing.