Bangkok: At first glance Rodrigo Duterte's order to deploy Philippine troops to 10 small islands and reefs in the flashpoint waters of the South China Sea is a serious escalation of a dispute that could engulf the world's major powers.

But like so many comments made by the 72-year-old firebrand President since he took office last June, it is unclear whether he is joking, stirring patriotic sentiments at home or is serious.

Taken at his word, sending the troops to build permanent structures like barracks and water desalination plants on the islands is a surprising reversal of his policy not to antagonise China. China in October pledged to invest $24 billion in the Philippines where poverty is widespread.

"It looks like everybody else is making a grab for the islands there, so we better live on those that are vacant," the President told reporters during a visit to a military camp on the western island of Palawan on Thursday.