China has called for the immediate release of twenty Chinese fishermen detained in the South China Sea by the Philippine navy on Sunday near a reef in the disputed Spratly Islands.

A foreign ministry spokesman Tang Guoqiang termed the arrests illegal and urged the Philippine government to make sure there was no repeat of the incident.

In October, the Philippines accused China of sending armed naval vessels to the area to build what it said were military structures.

The Chinese said they were fishermen's shelters and refused to take them down.