The stations have been placed on Fiery Cross, Subi and Mischief reefs of the Spratly (Truong Sa) Islands.
A South China Morning Post said the new stations could also be used for military purposes, but Chinese Foreign Ministry spokesman Lu Kang said at a press briefing on Thursday that they would mainly be used to ensure navigational safety in the South China Sea, as the waterway is known internationally.
The stations include equipment for basic ground and atmospheric observation as well as weather radars, which can be used together for constant monitoring of meteorological indicators, according to China’s state broadcaster CCTV.
Data collected by the stations will be used to provide more precise weather forecasts for the crews on fishing vessels and other ships in the region, it said.
Vietnam has repeatedly declared it has full legal basis and historical evidence to assert its sovereignty over the Spratly and Paracel (Hoang Sa) Islands.
In May, Vietnam's Foreign Ministry denounced China's installation of missiles on outposts in the Spratly Islands as a serious violation of its sovereignty in the waters.
A ministry spokesperson said the move increased tension and caused destabilization in the region, violated the Declaration on the Conduct of Parties in the South China Sea and was not beneficial to the negotiation of a Code of Conduct in the waters.
The ministry also voiced its objection after a CNBC report said that China had installed anti-ship cruise missiles and surface-to-air missile systems on Fiery Cross Reef, Subi Reef and Mischief Reef.
The act has been interpreted by experts as China pushing militarization in the waterway, which they said could invite counteractions from regional players, including the U.S. and Japan.
China seized the Paracels from South Vietnam by force in 1974 and has been illegally occupying a number of reefs in the Spratlys since 1988.
In recent years, China has illegally converted seven reefs in the Spratly Islands into artificial islands with runways capable of receiving military aircraft.