Construction of the lighthouses is being rushed, and will provide navigation services such as positioning reference, route guidance and navigation safety information to ships in the vicinity, the Xinhua News Agency reported.
The lighthouse on the east end of Meiji reef, which stands over 60 metres high, is the tallest of all the structures on the Nansha islands.
It emits white light at night with a range of over 20 nautical miles, Xue Anqing, deputy head of the China Communication 2nd Navigational Bureau, said on Monday.
The South China Sea is a critical maritime corridor linking the Pacific and Indian oceans, as well as it is a major fishing ground.
However, high traffic density, complex navigation conditions, a severe shortage in rescue forces have combined to threaten navigation safety and hinder regional economic and social development.
Construction of a lighthouse on Zhubi reef was completed in April.
A modern hospital will also be completed on Yongshu reef by the end of June. Remote technology will be used for consultations.