The US news network CNBC reported China had installed the weapon systems on three of the artificial reefs it had developed in the strategically vital waters.
"We know about the militarization of China in the South China sea".
Meanwhile, in a separate interview, US Ambassador to the Philippines Sung Kim told reporters also on Thursday, a day after CNBC released its report, "We are concerned anytime a claimant, including China, takes an aggressive unilateral action toward militarization".
Dr Euan Graham, the Director of International Security at the Lowy Institute in Sydney, says the latest manoeuvres in the Spratly Islands will force the U.S. and allies, including Australia, to reconsider before sending ships into the South China Sea.
On Thursday, White House Press Secretary also warned of "consequences" over the ongoing military buildup.
The land-based anti-ship missiles called YJ-12B can empower China to hit surface vessels within 295 nautical miles of the reefs while the surface-to-air missiles designated as HQ-9B can target aircraft besides nullifying drones and cruise missiles within 160 nautical miles, the CNBC report said.
The West Philippine Sea is the Philippines' exclusive economic zone in the South China Sea.
Similar systems have already been deployed in the Paracel islands, situated further to the north.
"The peaceful constructions of China in the Spratly archipelago, including the necessary deployment of defence facilities in the national territory, are aimed at protecting China's sovereignty and security, " said Hua Chunying.
According to US intelligence reports, the installations mark the first Chinese missile deployments to Fiery Cross Reef, Subi Reef and Mischief Reef in the Spratly Islands. China has to realise that they've benefited from the free navigation of the sea.
China yesterday defended the deployment of anti-ship cruise missiles and surface-to-air missile systems in the disputed waters, saying it has "indisputable sovereignty" over the area.
But this latest manoeuvre sends an implicit threat to other claimant nations that if they even try to exercise their rights to the Spratly Islands they will come within range of Chinese missiles.
The Chinese now lay claim to the Pratas, Paracels and Spratly islands, as well as the Macclesfield Bank area.
A USA official, speaking on condition of anonymity, said intelligence had seen some signs that China had moved some weapons systems to the Spratly Islands in the past month.
"Our policy in the South China Sea remains the same. Anyone with no invasive intention will find no reason to worry about this", the spokeswoman said. Vietnam, Philippines, Malaysia, Brunei and Taiwan have counterclaims. "We hope that the relevant party could view this matter in an objective and calm way".