China has used military drills it launched in protest against US House Speaker Nancy Pelosi's visit as a game plan to prepare for an invasion of Taiwan, the island's Foreign Minister says.

Joseph Wu made the comment in Taipei on Tuesday as Taiwan began its own military drills to test combat readiness, which involved firing howitzer artillery out to sea in the southern county of Pingtung.

It comes in response to ongoing Chinese exercises that have included launching missiles into waters off the island of 23 million people.

Mr Wu offered no timetable for a possible invasion of Taiwan, which is claimed by China as its own.

He said Taiwan would not be intimidated even as the drills continued with China often breaching the unofficial median line down the Taiwan Strait.

"China has used the drills in its military playbook to prepare for the invasion of Taiwan," Mr Wu said.

"It is conducting large-scale military exercises and missile launches, as well as cyberattacks, disinformation, and economic coercion, in an attempt to weaken public morale in Taiwan.

"After the drills conclude, China may try to routinise its action in an attempt to wreck the long-term status quo across the Taiwan Strait."

Such moves threatened regional security and provided "a clear image of China's geostrategic ambitions beyond Taiwan", Mr Wu said, urging greater international support to stop China from effectively controlling the strait.

A Pentagon official said on Monday that Washington was sticking to its assessment that China would not try to invade Taiwan for the next two years.

Mr Wu spoke as military tensions simmer after the scheduled end on Sunday of four days of the largest-ever Chinese exercises surrounding the island — drills that included ballistic missile launches and simulated sea and air attacks in the skies and seas surrounding Taiwan.

More China military drills to keep up pressure on Taiwan

China's Eastern Theatre Command announced on Monday that it would conduct fresh joint drills focusing on anti-submarine and sea assault operations — confirming the fears of some security analysts and diplomats that Beijing would keep up the pressure on Taiwan's defences.

Taiwan's Defence Ministry said it had detected 39 Chinese air force planes and 13 navy ships in and around the Taiwan Strait on Monday.

A person familiar with security planning in the areas around Taiwan described to Reuters on Tuesday a continuing "stand-off" around the median line involving about 10 warships each from China and Taiwan.

"China continued to try to press into the median line," the person said.

"Taiwan forces there have been trying to keep the international waterways open."

As Ms Pelosi left the region last Friday, China also ditched some lines of communication with the United States, including theatre-level military talks and discussions on climate change.

US President Joe Biden, in his first public comments on the issue since Ms Pelosi's visit, said on Monday he was concerned about China's actions in the region but he was not worried about Taiwan. 

"I'm concerned they are moving as much as they are," Mr Biden said in reference to China.

"But I don't think they're going to do anything more than they are."

Under Secretary of Defense for Policy Colin Kahl also said the US military would continue to carry out voyages through the Taiwan Strait in the coming weeks.

China has never ruled out taking Taiwan by force and on Monday, Chinese Foreign Ministry spokesman Wang Wenbin said that China was conducting normal military exercises "in our waters" in an open, transparent and professional way, adding Taiwan was part of China.

ABC/Wires