"1 PLA aircraft and 3 PLAN vessels around Taiwan were detected by 6 a.m. (UTC+8) today," Taiwan's Ministry of National Defence said in a statement.

"Armed Forces have monitored the situation and tasked CAP aircraft, Navy vessels, and land-based missile systems to respond to these activities," it added.

The statement came after Tsai met McCarthy in California during a stopover on her way back from a trip to Guatemala and Belize, which are among Taiwan's only 13 diplomatic allies.

China had threatened a "resolute" response to the meeting.

Taipei's Mainland Affairs Council, the island's top China policy-making body, on Wednesday accused Beijing of "obstructing" trade in the Taiwan Strait with on-site inspections on cargo and passenger ships.

Chinese maritime authorities had earlier said they were stepping up patrols in the waters separating the island from mainland China without providing more details.

"The Chinese side's action deliberately escalates cross-strait tensions," the MAC said.

"It is a clear violation of the cross-strait shipping agreement and maritime practice which will have a serious adverse impact on the normal traffic between the two sides."