Much to the chagrin of Beijing, the US senators took a military aircraft to Taiwan to announce vaccine donation.
China has lodged solemn representations with the United States over their visit, a Foreign Ministry spokesperson said.
Spokesperson Wang Wenbin told a press briefing that the visit of the US senators has gravely violated the one-China principle and the three China-US joint communiques that the United States once stated it would uphold.
Wang urged the US to immediately stop any form of official exchanges with Taiwan, handle the Taiwan question cautiously, and refrain from sending any wrong signals to "Taiwan independence" forces to avoid further serious damage to China-US ties and peace and stability across the Taiwan Strait.
US Senators Tammy Duckworth, Dan Sullivan and Christopher Coons made a rare visit to Taiwan, which China claims as part of it.
During their visit, Senator Duckworth said that the US will donate 750,000 Covid-19 vaccine doses to Taiwan as part of the country’s plan to share shots globally.
"It was critical to the United States that Taiwan be included in the first group to receive vaccines because we recognise your urgent need and we value this partnership," Duckworth said.
Taiwan, which recently witnessed sudden spurt of COVID-19 cases, has spurned China’s offer to supply its vaccines.
More than the vaccines, the biggest provocation for China is the US military aircraft parked on the runway, the CNN reported.
US senators are seen in front of the US Air Force C-17 Globemaster III freighter upon their arrival at Taipei's Songshan Airport.
The American delegation arrived at Taiwan's Songshan Airport on a US Air Force C-17 Globemaster III freighter - a primary strategic lift aircraft for the US military.
China opposes US arms sales to Taiwan.
On May 19, US navy’s guided-missile destroyer sailed through the Taiwan Strait, challenging China’s claims over the area as Beijing claims Taiwan as part of its mainland.
The US Navy’s 7th Fleet said in a statement "the ship’s transit through the Taiwan Strait demonstrates the US commitment to a free and open Indo-Pacific."
China is increasingly getting concerned over the US policy towards Taiwan.
China, for its part, vows to integrate the island with the Chinese mainland and it has stepped up military manoeuvres in the area. Beijing also firmly opposes the present Taiwanese President Tsai Ing-wen, who is a strong advocate of Taiwan’s independence.