A Chinese Naval officer stands guard beside a submarine at the Ngong Shuen Chau Naval Base in Hong Kong. Reuters

Beijing has upped the ante with its latest deployment of anti-ship cruise missiles and surface-to-air missile systems to fortified outposts in the hotly contested waters of the South China Sea. And it means China will likely soon send warplanes to the area, too, according to an expert on the region. "This should be seen as China crossing an important threshold. Missile platforms present a clear offensive threat," Gregory Poling, Center for Strategic and International Studies fellow and director of the Asia Maritime Transparency Initiative, told CNBC. "[The missile deployment] is a pretty clear threat to the other claimants and furthers China's goal of establishing complete control over the water and airspace of the South China Sea." According to U.S. intelligence reports, the installations mark the first Chinese missile deployments to Fiery Cross Reef, Subi Reef and Mischief Reef in the Spratly Islands. The Spratlys, to which six countries lay claim, are located approximately two-thirds of the way east from southern Vietnam to the southern Philippines.

Map of the South China Sea. CSIS Asia Maritime Transparency Initiative/CNBC

The land-based anti-ship cruise missiles, designated as YJ-12B, allow China to strike surface vessels within 295 nautical miles of the reefs. Meanwhile, the long-range surface-to-air missiles designated as HQ-9B, have an expected range of targeting aircraft, drones and cruise missiles within 160 nautical miles. Intelligence assessments say the missile platforms were moved to the outposts in the Spratlys within the past 30 days, according to sources who spoke on the condition of anonymity. "It has been clear that these were coming since at least last year when China constructed shelters for them at each of the islands, but the actual deployments are still significant," Poling said. "Now every ship or plane moving near the Spratlys is operating within Chinese missile range." While the installation of missile platforms are new to the Spratlys, China has already deployed similar systems in the nearby Paracel Islands. Satellite images of Woody Island, Beijing's military headquarters in the South China Sea, show deployments of Y-8 transport aircraft as well as J-10 and J-11 fighter jets.

CSIS Asia Maritime Transparency Initiative/DigitalGlobe