Beijing's biggest maritime drills in years involve about 60 warships and 30 coast guard vessels deployed from near 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 Taiwan, with 100 sorties detected over the past two days, according to figures from the island's defence ministry.

There has been no 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.

However, a recent Pacific tour by Taiwanese President Lai Ching-te that included two stops in US territory drew 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," the official said, referring to the chain linking Okinawa, Taiwan and the Philippines.

Taiwan's foreign ministry said Wednesday that China's increased military activity around the island was evidence that Beijing was a "troublemaker".

But China's foreign ministry -- whose spokesperson neither confirmed nor denied that drills were taking place -- directed blame at Taiwan.

"Harming the peace and stability of the Taiwan Strait is the work of Taiwan independence separatist forces, with the support of external actors," Mao Ning said Wednesday during a briefing in Beijing.

The United States was monitoring China's "latest activity" and would ensure "nobody does anything to change the status quo in the (Taiwan) Strait", US Defense Secretary Lloyd Austin told reporters at a US base in Japan Wednesday.

"We'll continue to do what we can to help Taiwan acquire the means to defend itself," he added.

- Simulating attacks, blockade -

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

Recent bad weather had "posed challenges for smaller vessels" involved in the drills, they said, adding that China also held "joint operations with Russia" in November.

Taiwan lives under the constant threat of invasion by China, which has not ruled out using force to bring the island under its control.

Beijing has ramped up the deployment of fighter jets and warships around the island in recent years, and also opposes any international recognition of self-ruled Taiwan -- especially when it comes to official contact between Taipei and Washington.

Lai spoke last week with Republican House Speaker Mike Johnson in addition to his two recent stopovers on US soil.

- 'Significantly larger' -

The security official said 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 two since Lai took office in May.

Beijing usually announces its military exercises but the official said one reason it may have decided to stay silent was to avoid overshadowing China's annual Central Economic Work Conference -- a closed-door leadership meeting scheduled Wednesday, according to reports.

Taipei-based military analyst Shu Hsiao-huang said Beijing's drills had a "pronounced sense of real combat readiness and operational intent ".

"In the East China Sea, it seems China is preparing for large-scale aerial operations to confront US naval forces," Shu told AFP.

"Meanwhile, the deployment of significant naval assets east of Taiwan suggests a strategy to blockade the island, cutting off its economic lifelines and essential resources."

Taiwan defence ministry's daily tally of Chinese aircraft detected around the island 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 were reported on October 15 after China staged large-scale military drills in response to Lai's National Day speech days earlier.