Up to 70 Chinese ships, including navy vessels, were monitored from the Yellow Sea to the South China Sea from May 1-27, a security official said on the condition of anonymity.

Beijing has ramped up the deployment of fighter jets and warships around Taiwan in recent years as it pressures Taipei to accept its claims of sovereignty over the island.

China has refused to rule out using force to bring Taiwan under its control, leaving the island to face the constant threat of invasion.

"Its military actions and grey-zone activities have included large-scale deployments across the entire island chain, involving comprehensive maximum pressure," the security official said in remarks released Monday.

"On average, there have been between 50 to 70 naval vessels and government ships as well as hundreds of sorties by various military aircraft continuously conducting harassment operations."

Some of the ships passed through the Miyako Strait to the Western Pacific Ocean for "long-distance training, including combined air-sea exercises", the official said.

Another 30 Chinese vessels with no name, documentation or port of registry were detected near Taiwan's Penghu archipelago in the Taiwan Strait on May 19 and had been "deliberately sent to harass", the official said.

And a total of 75 Chinese aircraft were involved in three "combat readiness patrols" near the island during the month, Taiwan's defence ministry figures show.

Asia-Pacific's so-called first island chain links Okinawa, Taiwan and the Philippines, while the Yellow Sea is west of South Korea -- all partners of the United States and critical to its influence in the region.

- 'More provocative' -

The Taiwanese security official said China's activities in May were "more provocative than previously observed".

In one incident, Tokyo and Beijing exchanged diplomatic protests each accusing the other of "violating" national airspace, after a Chinese helicopter and coast guard vessels faced off with a Japanese aircraft around disputed islands.

The Chinese actions were a demonstration of "military expansion" and were aimed at controlling the "entire island chain and improving their capabilities", the official said.

China's deployment coincided with Taiwanese President Lai Ching-te's speech on May 20 marking his first year in office and came ahead of an annual security forum in Singapore at the weekend.

US Secretary of Defence Pete Hegseth told the Shangri-La Dialogue that China was "credibly preparing" to use military force to upend the balance of power in Asia.

Beijing, which did not send its Defence Minister Dong Jun to the summit, warned Washington "should not play with fire".

"It felt like they were in a state where they could announce something at any moment, trying to seize on some opportunity or excuse to act," the Taiwanese official said of the Chinese.

China has carried out several large-scale military drills around Taiwan since Lai took office.