Taiwan's army held another live-fire drill Thursday after Beijing ended its largest-ever military exercises around the island and repeated threats to bring the self-ruled democracy under its control.

Beijing has raged at a trip to Taiwan last week by US House Speaker Nancy Pelosi -- the highest-ranking elected American official to visit in decades -- staging days of air and sea drills that raised tensions to their highest level in years.

Taiwan has accused China of using the Pelosi visit as an excuse to kickstart drills that would allow it to rehearse for an invasion.

Lou Woei-jye, spokesman for Taiwan's Eighth Army Corps, told AFP its forces fired howitzers and target flares as part of the defensive drill on Thursday.

The exercise in Taiwan's southernmost county Pingtung began at 08:30 am (0030 GMT) and lasted about an hour, he said.

Artillery tucked in from the coast was lined up side by side, with armed soldiers in units firing the howitzers out to sea one after the other, a live stream showed.

Taiwan held a similar drill on Tuesday in Pingtung. Both involved hundreds of troops, the military said.

The military has played down the exercises' significance, saying they were already scheduled and were not in response to China's war games.

"We have two goals for the drills, the first is to certify the proper condition of the artillery and their maintenance condition and the second is to confirm the results of last year," Lou said, referring to annual drills.

Taiwan routinely stages military drills simulating defence against a Chinese invasion.

On Thursday, Taipei's army said it detected 21 Chinese planes and six ships operating in the Taiwan Strait, without specifying if they were conducting operations.

Of those, 11 planes crossed the median line, an unofficial demarcation between China and Taiwan that Beijing does not recognise.

- 'Prepare for war' - Taiwan's president Tsai Ing-wen thanked troops in a visit to an air force command headquarters on Thursday.

"Right now, China's military threat has not lessened," she said in a statement posted on her Facebook page.

"I will reiterate, we will not escalate the conflict or cause disputes, we will firmly defend our sovereignty and national security, and defend the front line of democracy and freedom."

Taiwan's latest exercise came after China's military indicated its own drills had come to an end Wednesday, saying its forces "successfully completed various tasks" in the Taiwan Strait while vowing to continue patrolling its waters.

But in the same announcement, China said that it would "continue to carry out military training and prepare for war".

In a white paper published the same day, China's Taiwan Affairs Office said Beijing would "not renounce the use of force" against its neighbour and reserved "the option of taking all necessary measures".

"We are ready to create vast space for peaceful reunification, but we will leave no room for separatist activities in any form," it said in the paper.

China last issued a white paper on Taiwan in 2000.

Taiwan's Mainland Affairs Council, the island's top policymaking body on China, rejected the paper and said the document was "full of lies that are 'wishful thinking and disregarding the facts'".

Taiwan's foreign ministry on Thursday joined the council in rebuffing the "one country, two systems" model that Beijing has proposed for the island.

"China's whole statement absolutely goes against the cross-strait status quo and its reality," ministry spokesperson Joanne Ou told a press conference.

"China is using US House Speaker Nancy Pelosi's visit as an excuse to destroy the status quo and taking the opportunity to make trouble, attempting to create a new normal to intimidate the Taiwanese people."

The Chinese Communist Party's Taiwan Affairs Office said in a statement Thursday that Taipei's "rebellious actions are just a slap in the face and cannot stop the historical trend of reunification" with mainland China.

Pelosi has stood by her visit, saying Wednesday she was "very proud" of her delegation and believed China had used her visit as a "pretext" to launch its military exercises.

"We will not allow China to isolate Taiwan," Pelosi told reporters in Washington.

In response to the Chinese military revealing it was bringing drills to an end, Taiwan's army said it would "adjust how we deploy our forces... without letting our guard down".