An areal photo taken though a glass window inside a military plane of the alleged on-going reclamation by China into mischief reef in the Spratly group of islands in the South China Sea, west of Palawan, Philippines. Photo by RITCHIE B. TONGO / EPA

Aug. 23 (Asia Today) -- More than 200 Chinese vessels have gathered around Mischief Reef in the disputed South China Sea, raising concerns that Beijing may be preparing to tighten pressure on or eventually seize nearby Second Thomas Shoal, which is controlled by the Philippines, Japan's Asahi Shimbun reported Sunday.

According to private security analysis group DEEP DIVE, the number of Chinese vessels anchored at Mischief Reef in the eastern Spratly Islands rose sharply from fewer than 40 in mid-May to 80 on May 27. The number exceeded 150 in early June and reached 228 on July 3, Asia Today reported, citing the Asahi report.

Mischief Reef lies roughly 25 miles west of Second Thomas Shoal. The large concentration of vessels has raised concerns that China could use them to disrupt Philippine military resupply operations or as preparation for an attempt to seize the shoal.

The development has heightened military tensions in the South China Sea amid fears that China could repeat the approach it used at Mischief Reef, where it established control before constructing an artificial island and military facilities.