China doubled down on its threat to take countermeasures following US House Speaker Nancy Pelosi's visit to Taiwan, which both parties will "constantly feel".

China's Foreign Ministry Spokesperson Hua Chunying told reporters in Beijing a day after Pelosi's plane touched down on the island that Beijing claims as its own that the measures will be "resolute, forceful, and effective," and will "constantly" be felt by relevant authorities in the US and Taiwan.

"The nature of US House Speaker Nancy Pelosi's visit to the Taiwan region is not about democracy, but is an issue about China's sovereignty and territorial integrity," Hua said, according to Chinese broadcaster CGTN.

"Every time the US provoked China, the result has been a shame on themselves. The latest example was Pelosi instigating the black-clad riots in Hong Kong," she added.

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In a press during her visit, Pelosi said that "strength, goodwill and again, the demonstration of a democracy that has evolved to a stronger place now and offers a very strong contrast to what's happening in mainland China ... no more evidence needed than what happened in Hong Kong."

Beijing's warnings of retaliation against Washington come after Pelosi rejected Chinese warnings, including threats of military action, and went ahead with her trip to Taiwan, the first by a sitting US Congress speaker in 25 years.

She arrived in Taipei on Tuesday night and has been in continuous negotiations since this morning.

US will not abandon Taiwan

US House Speaker Nancy Pelosi left Taiwan on Wednesday following a visit that heightened tensions with China, saying she and other members of Congress in her delegation demonstrated their devotion to Taiwan.

Pelosi, the first US speaker to visit the island in more than 25 years, incurred Beijing's wrath and sparked a week-long debate over whether the visit was a wise idea once word of it leaked. 

Read next: China warns US will 'pay the price' if Pelosi visits Taiwan

“Today the world faces a choice between democracy and autocracy,” she said in a short speech during a meeting with Taiwanese President Tsai Ing-wen. “America’s determination to preserve democracy, here in Taiwan and around the world, remains ironclad.”

Pelosi arrived at a South Korean military camp on Wednesday evening, ahead of discussions with political leaders in Seoul and a visit to Japan. Both countries are US alliance members, housing approximately 80,000 American forces allegedly as a deterrent to North Korea's nuclear ambitions and China's growing influence in the South and East China seas.

Read next: US' Pelosi to travel to Asia

China announced a series of military exercises around the island, parts of which will enter Taiwanese waters, and issued a series of firm statements after the delegation arrived in Taipei on Tuesday night.