China has strongly condemned the United States for allowing Taiwanese President Tsai Ing-wen to visit Hawaii, and Beijing has vowed to take "firm countermeasures" against US arms sales to Taiwan.

This is the first stop on the Taiwanese leader's tour of several Pacific regions, a trip he presents as the beginning of a "new democratic era" but which has angered Beijing.

A Chinese Foreign Ministry spokesman said in a statement that his country strongly condemns the US organization of Lai's "transit" and has lodged a formal protest in this regard with Washington.

He stressed that "China will closely monitor the development of the situation and take resolute and effective measures to safeguard its national sovereignty and territorial integrity."

China considers self-ruled Taiwan part of its territory and opposes any international recognition of the island as a sovereign state

Lai is making his first overseas trip since taking office in May, and will visit the US islands of Hawaii and Guam, as well as three allied Pacific nations: the Marshall Islands, Tuvalu and Palau.

In a speech before his departure, Lai said the tour "ushers in a new era of values-based democracy" and thanked the U.S. government for "helping to make this trip smooth."

Arms sales to Taiwan

In addition to the Taiwanese president's tour, the US announcement on Friday that it had approved a deal with Taiwan to sell F-16 parts and radar systems worth an estimated $385 million appears to have angered China.

Beijing on Sunday expressed its "firm opposition" and "denounced" the US's approval of the sales to Taiwan.

In a separate statement, the Chinese Foreign Ministry urged the United States to "immediately stop arming Taiwan or encouraging and supporting forces that seek Taiwan's independence and want to strengthen its military to achieve this."

The statement added that China will take "strong and resolute countermeasures" to defend its national sovereignty, security and territorial integrity.

He also stressed that these sales represent a "serious violation" of China's sovereignty, noting that Beijing has lodged "stern representations" with Washington regarding the issue.

The US State Department had approved the deal, while the US Defense Security Cooperation Agency submitted the required notification to Congress on Friday.

The United States does not recognize Taiwan as a state but nevertheless provides significant military aid, which China opposes, accusing Washington of interfering in its affairs.

China considers Taiwan part of its territory, and has not been able to reunify it since 1949. Despite its "preference for peaceful reunification," it has not abandoned the principle of using military force, and regularly sends warships and fighter planes around this island.