Satellite images obtained by Reuters on Thursday show a build-up of Chinese civilian vessels near contested Thitu Island, Manila's key outpost in the South China Sea, but a senior Philippine navy officer said they are "not a cause for concern".

Thitu is a strategically important island from which Manila monitors Chinese vessels and aircraft in the busy waterway.

One of the images taken by Maxar Technologies on Monday and reviewed by Reuters shows about 60 vessels, some within 2 nautical miles of Thitu, a strategically important island from which Manila monitors Chinese vessels and aircraft in the busy waterway.

The Philippine Navy confirmed yesterday that dozens of Chinese military, coast guard and maritime militia vessels continue to swarm and stay in Subi Reef near Pag-asa Island in the West Philippine Sea (WPS) which China,