China has warned against those who are "expressing congratulations" to Taiwan's President-elect Lai Ching-te following his victory for the presidency of the self-governing island being claimed by Beijing to be its own.

Mao Ning, China's Foreign Ministry spokesperson, said Beijing already made "serious demarches" against those who praised the recent conduct of polls in the island as they supposedly meddled in the internal affairs of China and Taiwan.

The Department of Foreign Affairs (DFA), although it already repeated the Philippines adherence to the policy, has yet to clarify if the country is included among those issued demarches as President Marcos also congratulated Lai on his victory in a post on X on Monday night.

"China deplores and strongly opposes relevant countries' wrong practices violating the one-China principle, including issuing statements and 'expressing congratulations.' We’ve lodged serious démarches," Mao said.

Mao claimed that issuing a message of congratulations is not only violating the one-China principle but also meddling in China's "internal affairs and infringing upon China’s sovereignty."

She warned it could "face the joint opposition of the Chinese people and the international community."

"The elections of the Taiwan region are China’s internal affairs," she said.

Mao said the one-China principle is a political premise that establishes China's diplomatic relations with other countries. She said it is a "universally recognized basic norm in international relations and a prevailing consensus among the international community."

"Regardless of the result, the basic fact that there is only one China in the world and Taiwan is part of China will not be changed," she added.