Taiwan’s air force scrambled again on Monday to warn away 52 Chinese aircraft that entered its air defense zone, Taiwan’s defense ministry said, the largest number to date reported by Taipei and the fourth straight day of Chinese incursions.

Chinese-claimed Taiwan has complained for a year or more of repeated missions by China’s air force near the democratically governed island, often in the southwestern part of its air defense 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 defense 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.

The United States on Sunday urged China to stop its “provocative” military activities near Taiwan, while the island’s government has also condemned Beijing.

China has yet to comment. Calls to China’s Defense Ministry on Monday went unanswered. The country is in the middle of the week-long National Day holiday.