Hong Kong (CNN) Taiwan has accused China of "reckless and provocative" action, after two Chinese air force jets crossed a maritime border separating the island from the mainland.

The island's military scrambled fighter planes after it said two Chinese J-11 fighter jets crossed the border within the waters of the Taiwan Strait, known as the median line, at about 11 a.m. on Sunday.

"Two PLAAF J-11 jets violated the long-held tacit agreement by crossing the median line of the Taiwan Strait. It was an intentional, reckless and provocative action. We've informed regional partners and condemn China for such behavior," the Taiwan Ministry of Foreign Affairs said in a statement

If confirmed as intentional, the Chinese incursion would be the first of its kind in years, said Bonnie Glaser, director of the China Power Project at the center of Center for Strategic and International Studies.

"Chinese jets flew across the center line frequently in 1999," Glaser said. "Since then, there have been occasions when PRC jets flew toward the center line and then veered off. They haven't crossed it in a long time. By some accounts 20 years."