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, last 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.

"I have ordered the armed forces to occupy all… At least, let us get what is ours now and make a strong point there that it is ours," he said.

The remarks are sure to provoke an angry response from China, which claims almost all the strategically important parts of the South China Sea where US$5.3 trillion in trade passes each year.

It is unclear how Mr Duterte's order could be executed. Some of the islands would need expensive and logistically difficult reclamation work before structures could be built on them. China could block supplies to the islands by stationing its Coast Guard vessels in waters near islands it occupies.

Analysts trying to interpret Mr Duterte's often expletive-ridden and inflammatory comments on many issues wonder whether he is making a policy statement or another of his high-stakes quips.

When he was campaigning for president he said he would ride a jet-ski to an island in the South China Sea and raise the Philippine flag.

He later mocked the media for taking his claim seriously.

On Thursday Mr Duterte told his troops that he may visit one of the islands on the Philippine Independence Day in June to raise the flag.

Asked about his plans for a rusty ship that serves as outpost in the South China Sea for a handful of Philippine marines, he said "I will replace it with a luxury liner. There will be waiters, food, swimming pool so the soldiers there can get fat."

The man who likes to be called "The Punisher" also told the troops never to surrender to the enemy.

"On the last bullet, put the pistol to your head and tell the enemy 'f--- you.' At least you will die with your dignity," he said.

Carlyle Thayer, an expert on the South China Sea at the University of New South Wales' Australian Defence Force Academy, said it was quite clear that China's continued consolidation of control over and militarisation of islands in the disputed waters has unnerved Filipino defence officials and now the President.

China has recently fortified its three main islands with airfields, hangers for military jets and installed missile weapons systems and anti-aircraft guns.

Professor Thayer said the Philippines was spooked by reports, later denied by Beijing, that China was moving to install environmental monitoring equipment on to Scarborough Shoal seaized by China in 2012. The shoal sits only 12 nautical miles from the Philippine coast.

Manila also raised concerns when a Chinese oceanographic ship plied waters in the Benham Rise off Philippines' east coast.

Richard Javad Heydarian, an assistant professor of political science at Manila's De La Salle University, said Mr Duterte's comments were meant to calm nerves within the Philippine defence establishment.

"He definitely felt the heat, so is now scrambling to build his patriotic credentials," he said.

Professor Thayer pointed out the Philippines will violate a 2002 declaration among claimant nations in the South China Sea to exercise self-restraint if it does occupy the islands.

"Even more serious, China is likely to respond. Chinese officials have been quoted as saying 'if you do one, we will do one and a half. If you do two, we will do two and a half," he said.