Beijing's biggest maritime drills in years involve about 60 warships and 30 coast guard vessels deployed around the southern islands of Japan to the South China Sea, a senior national security official told AFP on the condition of anonymity.

China has also ramped up military aircraft activity closer to the island, with 100 sorties detected over the past two days, figures from the Taiwan defence ministry show.

There has been no public announcement by Beijing's army or Chinese state media about increased military activity in the East China Sea, Taiwan Strait, South China Sea or Western Pacific Ocean.

But a recent Pacific tour by Taiwanese President Lai Ching-te had included two stops in US territory, drawing fury from Beijing, which claims the democratic island as part of China's territory.

The security official said Wednesday that China's plans for the massive maritime operation began in October, and were aimed at demonstrating that Beijing could choke off Taiwan and also to "draw a red line" ahead of the next US administration.

"China uses President Lai's overseas visit as a pretext, with Taiwan only serving as an excuse," the official said.

"The real objective appears to be asserting control within the first island chain and establishing strategic deterrence ahead of the US presidential transition."

- Simulating attacks, blockade -

During the drills, Chinese warships have simulated attacking foreign ships while the coast guard has practised intercepting commercial vessels as well as disrupting and blockading sea routes, the official said.

China also held "joint operations with Russia" over several days in November, the official said.

Recent bad weather had "posed challenges for smaller vessels" involved in the drills, they said.

Taiwan regards itself as a sovereign nation. China has said it will not rule out using force to bring the self-ruled island under its control, and has ramped up the deployment of fighter jets and warships around Taiwan in recent years to press its claim.

China also opposes any international recognition of Taiwan and especially bristles at official contact between Taipei and Washington.

Lai made two stopovers on American soil as part of his Pacific tour last week and spoke with Republican House Speaker Mike Johnson, which drew a barrage of criticism from China.

Beijing's foreign ministry spokeswoman said Tuesday that China will "resolutely defend" its sovereignty.

The sea drills were "significantly larger" than Beijing's maritime response to then-US House speaker Nancy Pelosi's visit to Taipei in 2022, which was China's largest-ever war games around Taiwan.

China has held four major military exercises in just over two years, including the drills in response to Pelosi's visit and two since Lai took office in May.

The defence ministry's daily tally of Chinese aircraft detected around Taiwan was 53 on Wednesday and 47 on Tuesday.

Wednesday's figure was the highest number of aircraft detected in a single day since a record 153 was reported on October 15 after China staged large-scale military drills in response to Lai's National Day speech days earlier.