Philippine President Rodrigo Duterte has threatened to send troops on a 'suicide mission' if Beijing refuses to 'lay off' a disputed island in the South China Sea.

Duterte said he has been left with few options by the Chinese manoeuvres in the region.

In a speech on Thursday night Duterte said: 'I will not plead or beg, but I'm just telling you lay off Pag-asa because I have soldiers there.

He added: 'If you touch it, that's another story. Then I will tell my soldiers "prepare for suicide missions."'

The disputed Pag-asa (Thitu Island) in the South China Sea, President Duterte has warned China that if they touch the island he may be forced to send his military on a 'suicide mission'

Philippine President Rodrigo Duterte speaks at the Presidential Palace in Manila in October 2018

He reminded China of the closer ties that had been forged under his leadership but warned if the disputed island was threatened 'things would be different.'

Duterte has adopted a non-confrontational approach in territorial spats with Beijing while seeking Chinese infrastructure funds, trade and investment.

He has often lashed out at the security policies of the United States, a treaty ally, while praising China and Russia.

Duterte has often had to walk a tightrope when discussing China's increasingly assertive actions in the disputed waters, where Manila and Beijing, along with four other governments, have wrangled for control.

The Philippine Department of Foreign Affairs on Thursday issued a rare public rebuke of large numbers of Chinese vessels near islands and islets occupied by the Philippines in the disputed waters, saying the Chinese presence was illegal.

The Philippine military has monitored more than 200 Chinese vessels from January to March in a disputed area named Sandy Cay near a Philippine-occupied island called Pag-asa by Filipinos.

'I'm trying to tell China, Pag-asa is ours ... so let us be friends but do not touch Pag-asa Island and the rest. Otherwise, things would be different,' Duterte said. 'This is not a warning, this is just a word of advice to my friends, because China is our friend.'

When he first met President Xi Jinping in Beijing in 2016, Duterte said he told him, 'We are staking our claim in our economic zone and we will dig for oil in our territory.'

But Duterte said the Chinese leader replied that it was better to hold talks first because 'if you insist on your position, there might be trouble.'

'I had no choice,' Duterte said. 'If I send my navy and my soldiers there tomorrow and start to travel toward them, in a matter of seconds they'll all explode ... they will be slaughtered and the missiles that are parked there will arrive in Manila in about four minutes. Do you want a war?'

Chinese President Xi Jinping speaks after reviewing the Chinese People's Liberation Army Navy fleet in the South China Sea in April 2018

Filipino soldiers stand at attention near a Philippine flag at Pag-asa (Thitu island) in disputed the South China Sea in April 2017

Duterte said the Americans would comply with their obligations under their Mutual Defense Treaty with Manila but that they need congressional permission before going to war. 'Do I trust the Americans? Yes. But will that help be on time? That's the problem,' he said.

He raised anew his criticism of America for failing to stop China's transformation of seven disputed reefs into islands, some of them with runways, in the South China Sea. After he took office in 2016, Duterte said the Chinese islands had become 'military garrisons.'

'Why was it not stopped by America?' Duterte asked.