TAIPEI (REUTERS, AFP) - Taiwan reported the largest ever incursion by China's air force into its air defence zone on Monday (Oct 4) at 52 aircraft in the day and another four at night, saying the Taiwanese air force had to scramble for the fourth straight day to warn off the intruders, as tensions spiralled.

Taiwan has complained for a year or more of repeated missions by China's air force near the democratically governed island, often in the south-western part of its air defence zone close to the Taiwan-controlled Pratas Islands.

But since Friday, when China marked its national day, the country has embarked upon a massive ramping up of its missions, with almost 150 aircraft flying into the defence zone over the space of four days.

The latest mission included 34 J-16 fighters and 12 nuclear-capable H-6 bombers, which all flew in an area in the vicinity of the Pratas Islands, according to a map provided by the ministry.

Taiwanese fighter jets scrambled to warn away the Chinese planes, while missile systems were deployed to monitor them, it added.

Taiwan's government demanded on Monday that China immediately stop "irresponsible provocation" against the island.

Taiwan's Cabinet-level Mainland Affairs Council said in a statement that China was the "chief culprit" in creating tensions across the Taiwan Strait.

US State Department spokesman Ned Price on Sunday urged China to stop its "provocative" military activities near Taiwan.

China's foreign ministry on Monday said the US should stop supporting "separatist forces" backing an independent Taiwan and warned that Beijing would take all necessary measures to "crush" any independence plots.

China regards Taiwan as a renegade province to be reunified, by force if necessary.

In a statement issued a day after the US urged China to stop "provocative" military activities near Taiwan, Chinese foreign ministry spokesman Hua Chunying said China's determination and will to defend its national sovereignty and territorial integrity is unwavering.

The US Department of Defence said on Monday that China's increasing military activities conducted near Taiwan are destabilising and increase the risk of miscalculation.

"Our commitment to Taiwan is rock-solid and contributes to the maintenance of peace and stability across the Taiwan Strait and within the region," it said in a statement.

Taiwan has termed China's activities as "grey zone" warfare, designed to wear down Taiwanese forces and test their abilities.

A Taiwan-based source familiar with security matters in the region told Reuters earlier on Monday the Chinese planes were possibly conducting simulated attacks on US carrier fleets, drills the source said that China has repeatedly carried out near Taiwan in the past few months.

The carrier the USS Ronald Reagan entered the South China Sea late last month.

On Monday, Japan's defence ministry said that ship, along with another carrier the USS Carl Vinson, had carried out multinational joint exercises in waters south-west of Okinawa, though it gave no exact location.

Okinawa is home to a major US military base and lies just to the north-east of Taiwan.

The start of China's activities might also be deliberately timed as "intimidation" before Japan unveiled a Cabinet under new prime minister Fumio Kishida, the source added.

Mr Kishida unveiled his Cabinet earlier on Monday. A Japanese defence ministry official declined to comment.

"Although we watch developments between China and Taiwan closely, we do not comment on each one of them," the official told Reuters.

China has previously said such flights were to protect its sovereignty and aimed against "collusion" between Taiwan and the US, the island's most important international backer and arms supplier.

Taiwan, which will celebrate its national day on Sunday (Oct 10), says it will defend its freedom and democracy.