Beijing, which claims self-ruled Taiwan as part of its territory, neither confirmed nor denied the manoeuvres.

Taiwan's defence ministry and other security agencies were monitoring China's activities and had a "complete grasp of the situation", Presidential Office spokeswoman Karen Kuo told reporters.

She did not say how many Chinese ships were involved in the deployment, but a security source told AFP the number was "significant". The source spoke on condition of anonymity because they were not authorised to speak to the media.

The operations were not limited to the Taiwan Strait, but extended from the southern Yellow Sea, to the East China Sea near the disputed Diaoyu Islands and on into the South China Sea and even the Western Pacific, Kuo said.

"This indeed poses a threat and impact on the Indo-Pacific and the entire region," she said.

Taiwan urged China to "exercise restraint", Kuo said, adding: "We are also confident that we can handle this matter well."

Neither China's armed forces nor state media have announced any increased military activity in the region where Taiwan said Chinese ships had been detected.

Beijing's defence ministry spokesman Jiang Bin said Friday that the navy's training on the high seas complies with international law and "is not directed at any specific country or target".

He was responding to a question about a Chinese naval flotilla that reportedly may be heading towards Australia.

A spokesman for China's foreign ministry said Beijing "has consistently followed a defensive policy" and urged "relevant parties" not to "overreact or... engage in groundless hype".

China has refused to rule out using force to take Taiwan, and also contentiously claims nearly all of the South China Sea.

Taiwan's intelligence chief Tsai Ming-yen said Wednesday that October to December was the "peak season" for China's "annual evaluation exercises".

There was a possibility that China's ruling Communist Party could turn seemingly routine military activities into drills targeting Taiwan, Tsai warned.

Taiwan's defence ministry reported at 7:00 pm (1100 GMT) that it had detected 24 Chinese military aircraft near Taiwan since 2:22 pm, including 19 that crossed the median line of the Taiwan Strait to participate in a joint combat patrol with navy ships.

Last December, Taiwan said about 90 Chinese warships and coast guard vessels took part in vast exercises including simulating attacks on foreign ships and practising blockading sea routes in Beijing's biggest maritime drills in years.

Beijing did not confirm the drills at that time.

The United States has long been Taiwan's most important security backer and biggest supplier of arms.

But President Donald Trump's administration signalled a potential shift in that policy on Friday, saying in a strategy document that its Asian allies Japan and South Korea should take on more of the burden of defending the region.