On Sunday, the government of the Philippines asked the Chinese ambassador to explain why a growing flotilla of Chinese boats is surrounding the disputed Scarborough Shoal.

“There were four Chinese coastguard ships and six other vessels, including blue-coloured barges, around Scarborough Shoal. The presence of many ships other than coastguard in the area is a cause of grave concern,” said Defense Secretary Delfin Lorenzana, in a statement Reuters reports was delivered to reporters via text message.

The tiny Scarborough Shoal is a rich fishing ground, traditionally worked by fishermen from China, Vietnam, and the Philippines. It was specifically addressed by the recent international arbitration court ruling that struck down China’s claims to the area.

“China has refused to recognize the ruling and the latest comment from the Philippines could cause a stir ahead of a regional summit in Laos starting on Tuesday, where leaders of Southeast Asian states as well as China, Japan and United States will meet,” Reuters anticipated.

The barges reported by Defense Secretary Lorenzana are a matter of particular concern because dredging barges have been the first step in Chinese land-reclamation projects in other disputed areas it claims, such as the Spratly islands. Subsequent steps might involve turning the upgraded islands into a Chinese military outpost.

“If they try to construct anything in Scarborough, it will have [a] far-reaching adverse effect on the security situation,” Lorenzana warned, according to the Wall Street Journal.

The Journal also has a response from the Chinese Foreign Ministry, which said China has “maintained a Coast Guard patrol and there are some fishing boats undertaking fishing operations in the area. The situation hasn’t changed. We hope it won’t be hyped up, and that both sides can work together to build trust.”

This crisis is brewing while President Obama is visiting China for the G20 summit, and Philippine president Rodrigo Duterte is preparing for a bilateral meeting with the U.S. president at an ASEAN summit in Laos tomorrow — timing that makes the news from the Scarborough Shoal “tough to ignore,” in the estimation of the Washington Post.

“Most believed China would wait until after this week’s G20 meetings, or even after the U.S. presidential election, to make any move. The fact that new ships were reported the day before China’s Xi Jinping had tea with President Obama in Hangzhou is therefore something of a surprise,” the Post writes.

It is only a surprise to those who do not understand that China’s agenda involves sending a message that Barack Obama presided over the end of the American century, and there are new dominant powers in every quarter of the globe.

Duterte seems on the cusp of getting the message. The WSJ notes that he has “generally shunned international diplomatic norms” and used “off-color language” to slam his adversaries, most recently referring to Barack Obama as a “son of a whore” because Obama dared to criticize his war on crime. But he has been more “circumspect” with China, even as territorial disputes in the South China Sea generate real tension between Beijing and Manila.

Duterte reportedly wailed, “Why is China treating us this way?” when he was shown the latest surveillance photos of the Scarborough Shoal.

He will get the idea soon enough: It is all about establishing Chinese dominance and demonstrating the Obama administration’s impotence, before China and the Philippines enter negotiations about the South China Sea, later this year.

China supposedly backed down from developing the Scarborough area after Obama expressed U.S. opposition to their plans in March, in part because thousands of Americans are scheduled for deployment in the Philippines as part of a new defense agreement, and having a Chinese military outpost only 140 miles from Luzon would be disturbing.

China wants to let Duterte know that development of that military base is still very possible, and it could happen very quickly. A moment of tension between Duterte and Obama is the perfect time for China to remind the Philippine leader that it’s no longer the same world it was in 2008.