Taiwan President Tsai Ing-wen has said her country is not intimidated by China's latest military drills this week.

China's People's Liberation Army said its warships, bombers and reconnaissance aircraft had conducted "necessary drills" around Taiwan on Monday, though it described them as routine.

"We will not make any compromise on our territory for even one inch. We always hold on tight to our democracy and freedom," Tsai told reporters at an event to mark Taiwan-US ties in Taipei.

Taiwan scrambled jets and ships to monitor the Chinese forces on Monday, its defence ministry said, accusing Beijing of "trying to change the status quo of the Taiwan Strait".

China has repeatedly carried out what it calls "island encirclement patrols" in the past few years.

A delegation led by former US speaker of the House of Representatives, Paul Ryan, is in Taipei to mark 40 years since the signing of the Taiwan Relations Act, which governs US-Taiwan relations, and to reaffirm Washington's commitment.

The United States has no formal ties with Taiwan but is bound by law to help provide the island with the means to defend itself and is its main source of arms.

Ryan said the US considers any military threat to Taiwan a concern and urged China to stop, saying the moves were counterproductive.

The United States has no formal ties with Taiwan but is bound by law to help provide the island with the means to defend itself and is its main source of arms.

Beijing suspects Taiwan's president is pushing for the island's formal independence, a red line for China which has never renounced the use of force to bring Taiwan under its control.

Tsai says she wants to maintain the status quo with China but will defend Taiwan's security and democracy.

Last month, Washington sent Navy and Coast Guard ships through the narrow strait separating the island from the mainland, part of an increase in the frequency of US movement through the strategic waterway to show support for Taipei.