Chinese warships have regularly patrolled waters within the South Korean Navy's operational zone in the Yellow Sea without prior notification, multiple sources in Seoul said Sunday, sparking worries over the Asian power's growing naval presence.

   China's destroyers and escort vessels have entered the so-called area of operations (AO) under the Korea Air Defense Identification Zone (KADIZ) in the Yellow Sea once or twice a week to conduct search maneuvers, the military sources said. They did not specify when the patrols started.

   The KADIZ was designated by the commander of the U.S. Pacific Air Force Command in 1951 to prevent air clashes between nations surrounding the Korean Peninsula. Although the area is not South Korean airspace, the country's military supervises the zone and foreign aircraft must receive approval from the military 24 hours prior to entering the zone.

   "There is no international regulations to force out foreign ships that enter the AO," a source said, asking for anonymity due to the sensitivity of the issue. "Although Chinese authorities claim it is part of their normal maritime operations, it effectively means that they don't recognize the AO."

   The tensely guarded western sea was the scene of several deadly skirmishes with North Korea in the 1990s and early 2000s. Most recently, tensions escalated after Pyongyang torpedoed a South Korean warship in March 2010 and shelled Yeonpyeong Island eight months later, killing 50 South Koreans that year.

   Another military source said the patrols illustrate China's growing naval presence in waters near the Korean Peninsula and Japan, calling attention to the Liaoning, China's first aircraft carrier which was recently deployed to the eastern port city of Qingdao.

   "China's regular patrols within (South Korea's AO) and increasing naval capacity seem connected to (the Liaoning's deployment to Qingdao)," the source said.

   The patrols come at a time when Beijing and Tokyo are at odds over territorial disputes and other Asian countries have expressed concern over China's growing naval strength in the region.

   The Asian giant's latest military move sparked concern over the South Korean Navy's lack of capacity to handle long-range missions, with its role mostly limited in defense against North Korea.

   South Korea's Navy chief earlier this month vowed to strengthen naval forces to cope with rising tensions in Northeast Asia, in light of the ongoing territorial disputes between China and Japan.

   Adm. Choi Yoon-hee said the Navy will push to create two more naval task forces in the next two decades to respond to provocations from North Korea and safely protect its territory. (Yonhap News)