Twenty Chinese warplanes entered Taiwan's air defense identification zone on Friday, the self-ruled island's Defense Ministry said, with Reuters calling it the largest incursion yet reported.

The Chinese activity was likely a response to Thursday's signing of a memorandum of understanding between the United States and Taiwan to boost cooperation between their coast guards.

The warplanes involved in the intrusion included 10 J-16 fighter jets and four H-6K bombers, according to the Taiwan ministry. Some aircraft even crossed the Bashi Channel into airspace east of the island.

According to Reuters, it marked the largest incursion to date by the Chinese air force since Taiwan's defense ministry began disclosing near-daily Chinese military flights over the waters between the southern part of Taiwan and the Taiwan-controlled Pratas Islands in the South China Sea last year.

China's increasing pressure on the island, which Beijing regards as a renegade province awaiting reunification by force if necessary, has been a source of concern in the United States.

Through unofficial relations with Taipei, the United States has continued to assist the democratic island in maintaining a sufficient self-defense capability.

The memorandum agreed between the United States and Taiwan was on the establishment of a "Coast Guard Working Group," according to the Taipei Economic and Cultural Representative Office in Washington, Taiwan's de facto embassy in the United States.

The group will serve as a platform for both sides to coordinate efforts focused on improving communications and sharing information.

The U.S. and Taiwan coast guards have worked closely together on issues including maritime search and rescue and fisheries enforcement, but the working group is expected to advance bilateral cooperation toward a "free and open Indo-Pacific" region, TECRO said on its website.

The move came after China implemented in February a law that allows its coast guard to use weapons against foreign ships that Beijing sees as illegally entering its waters, raising fears of escalation of maritime disputes in the East and South China seas.