By Ryan Woo, Ben Blanchard and Yimou Lee
BEIJING/TAIPEI (Reuters) -China said on Wednesday it takes "necessary measures" to defend the country's sovereignty and will not tolerate "separatist" activities, as Taiwan reported another rise in Chinese warplanes around the island and called on Beijing to halt provocations.
Beijing's military has yet to comment on the military activity and has not confirmed it is carrying out exercises.
A senior Taiwanese official said they believed the surge in activity was meant to send a political message to the incoming administration of U.S. President-elect Donald Trump.
A security diplomat in the region briefed on the matter told Reuters the scale and size of the ongoing Chinese operations, including the manpower being dispatched, was "unheard of" in recent years.
"We have not seen anything like this in at least the past few years," they said citing their country's assessment while declining to be identified given the sensitivity of the matter.
China, which views democratically governed Taiwan as its own territory, had been expected to launch drills to express its anger at President Lai Ching-te's tour of the Pacific that ended on Friday and included stopovers in Hawaii and the U.S. territory of Guam.
"We will absolutely not let things go unchecked. We take necessary measures to resolutely defend the country's sovereignty and territorial integrity," Zhu Fenglian, a spokesperson for China's Taiwan Affairs Office said when asked about the increased military activities.
China's government was "highly vigilant to the trend of separatist Taiwan forces colluding with external forces", she said at a regular news briefing in Beijing.
Taiwan's defence ministry said on Wednesday it had detected 53 military aircraft operating around the island over the past 24 hours, as well as 11 navy vessels and eight "official" ships, which refers to vessels from ostensibly civilian agencies such as the coast guard.
"PROVOCATIVE ACTS"
Lai and his government reject Beijing's sovereignty claims, saying only Taiwan's people can decide their future.
Presidential office spokesperson Karen Kuo said in a statement that China's military actions were a "blatant disruption" of regional stability and Beijing should immediately stop all "provocative acts".
It is customary for Taiwan presidents to go overseas and "Taiwan's normal international exchanges with other countries are not an excuse for China's provocations", she added.
Taiwan's military had gone on alert on Monday after saying China had reserved airspace and deployed naval and coast guard vessels.
On Tuesday, Taipei's defence ministry said China was deploying its largest navy fleet in regional waters in nearly three decades, posing a threat to Taiwan that is more pronounced than previous Chinese war games.
However, a U.S. military official said China's naval deployments in the East China Sea and South China Sea were elevated but consistent with other large exercises in the past.
A senior Taiwan security official, offering the government's assessment of China's activities, told a briefing in Taipei it took China's military nearly 70 days to plan and deploy the current sea operations and that they were meant for the incoming Trump government and U.S. allies, rather than specifically Lai's visit to the Pacific.
"They are trying to draw a red line and exert authority for the new master of the White House," the official said, who spoke on the condition of anonymity.
It was "extremely rare" for China to deploy sea operations of such scale at this time of the year when sea conditions are usually rough, the official said.
Taiwan's government believes China's decision not to announce the drills could be because Beijing is trying to minimise the impact on two major events with Taiwanese businessmen and politicians, one taking place this week and another next week, the official added.
"It's a carrot and stick approach," the official said, pointing to Beijing's annual charm offensive programmes towards Taiwan, including a visit to Taipei by one of Shanghai's deputy mayors next week.