Tensions between Beijing and Manila over the South China Sea have risen another notch after the Philippines' Foreign Secretary published an obscene tweet to order Chinese ships to leave the disputed waters. 

"China, my friend, how politely can I put it? Let me see.... O.... GET THE F*** OUT," tweeted Teodoro Locsin, who is known for colourful language on social media. 

"What are you doing to our friendship? You. Not us. We're trying. You. You're like an ugly oaf forcing your attentions on a handsome guy who wants to be a friend; not to father a Chinese province ..." 

The Foreign Secretary's expletive-riddled language is the latest in an escalating row between the nations over the continued incursion of Chinese coastguard ships and fishing boats into resource-rich waters inside the Philippines' 200 nautical mile Exclusive Economic Zone (EEZ). 

An international tribunal invalidated China's claim to 90 per cent of the South China Sea in 2016, but Beijing has never recognised the ruling and calls it "a sham". 

At one point, at least 220 Chinese vessels had massed around the Whitsun Reef in the Spratly Islands, where in recent years Beijing has built military installations on a string of reefs and semi-submerged islands. 

China insists it owns the reef, and the vessels were fishing boats seeking shelter from the rough seas, despite strong evidence that many were part of a Chinese-armed maritime militia.

The Philippine government says the reef — which it calls Julian Felipe — is within an internationally recognised offshore zone where Manila has exclusive rights to fish and exploit oil, gas and other resources. 

'Suave diplomatic speak gets nothing done'

Ben Bland, director of the Lowy Institute's South-East Asia project, said it was unlikely China would see the Foreign Secretary's intemperate language as a massive escalation in tensions. 

"I think Chinese officials will kind of see it in the spirit of [Mr Locsin's] other tweets." 

China's embassy in Manila has not immediately responded to the comments. But Beijing has ignored repeated demands to remove its vessels and accused Manila of escalating the dispute, though many of the vessels have since gone. 

Tensions reached a head last week when the Philippines coastguard began maritime exercises to boost its presence in disputed waters and to counter the presence of Chinese boats. 

In response to criticism of his comments by other Twitter users, Mr Locsin tweeted that "usual suave diplomatic speak gets nothing done." 

In a separate statement, the Philippines Department of Foreign Affairs accused China's coastguard of "shadowing, blocking, dangerous manoeuvres, and radio challenges" of its own coastguard vessels near the disputed Scarborough Shoal, which the Philippines calls Bajo de Masinloc. 

"China has no law enforcement rights in these areas. The presence of Chinese coast guard vessels in the Philippines' territorial waters ... and exclusive economic zones, raises serious concerns.

"The unauthorised and lingering presence of these vessels is a blatant infringement of Philippine sovereignty." 

'They probe for weakness'

Ben Bland said China was not worried about unilateral statements of condemnation from any South-East Asian nation or rival claimants to its maritime territory or resources. 

"If you look at China's tactics in the South China Sea over the last decade or so, it's really a case of probing for weakness," he said.

"They're trying to advance the ambit of the waters that they're able to control. They're trying to secure more access to fisheries resources ... eventually, oil and gas."

But Mr Bland said part of China's strategy is taking into account how their rivals respond to their actions in the South China Sea. 

"We often have seen that when China has had pushback, they take a pause, and they probe for weakness in another location," he said. 

"And all the while, of course, they've been building up their naval forces, their fishing fleet, their militia, their marine militia, as well." 

Philippines' Defence Secretary Delfin Lorenzana said his government would continue to patrol and defend the nation's waters. 

"While we acknowledge that China's military capability is more advanced than ours. This does not deter us from defending our national interest, and our dignity as a people, with all that we have," he said. 
 
"The government will not waver in its position." 

Sea dispute puts Duterte in an awkward position 

The worsening feud has escalated despite President Rodrigo Duterte's policy to forge stronger ties with Beijing. 

As members of his own government condemned China's actions in the South China Sea, Mr Duterte has been reluctant to speak out against a country he sees as a source of billions of dollars in investment and aid. 

While insisting the Philippines would not compromise on its sovereignty, Mr Duterte last week cited Manila's "debt of gratitude" to Beijing, for donating hundreds of thousands of doses of vaccine against COVID-19. 

"China remains to be our benefactor. Just because we have a conflict with China does not mean to say that we have to be rude and disrespectful," Mr Duterte said in a weekly national address.

"So, kindly just allow our fishermen to fish in peace and there is no reason for trouble."