Red tarpaulin banners with the words, in English: "Welcome to the Philippines, Province of China" mysteriously appeared on footbridges across the capital Manila on Thursday.
It was not immediately clear who put them up or why, but the banners' appearance coincides with the anniversary of an international court ruling against Beijing in a dispute over waters in the South China Sea.
Dealing a major blow to China, the intergovernmental, dispute-resolution Permanent Court of Arbitration (PCA-CPA) in The Hague ruled two years ago that Beijing had no historic title to waters in the South China Sea.
It found that China had breached the Philippines' sovereign rights by blocking its fishing boats and building artificial islands in its Exclusive Economic Zone.
The banners, with the words: "Welcome to the Philippines, Province of China," stirred anger among Filipinos who vented their fury on social media.
Former Solicitor General Florin Hilbay, who was the chief lawyer for the Philippine PCA-CPA case, said the banners were "NOT FUNNY."
President Rodrigo Duterte, who took office just two weeks before the PCA-CPA ruling, has since taken a conciliatory approach towards China and has not pressed Beijing to implement the verdict.
By contrast, he frequently praises Chinese President Xi Jinping. In February, he controversially joked about offering the Philippines to Beijing as a province of China.
But opposition party Akbayan said Duterte scored an "own goal" by failing to insist that Beijing leave the ocean areas claimed by the Philippines.
Some social media users accused the opposition of being behind the banners to discredit the government's increasingly warm ties with China.
Duterte's spokesman, Harry Roque, called the banners "absurd" and blamed them on the government's political enemies.
City authorities were seen removing some of the banners, which were spotted in at least five locations.
ap/jm (Reuters, dpa)
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