Taipei said on Wednesday it had detected 45 Chinese military aircraft around Taiwan, the highest single-day number this year and coming less than a week before the self-ruled island inaugurates its new president who China regards as a "dangerous separatist".

China claims democratic Taiwan as part of its territory and has said it would never renounce the use of force to bring it under Beijing's control.

It has warned that Lai Ching-te, the current vice president who will be sworn into Taiwan's top post on 20 May, would bring "war and decline" to the island, and tensions have soared since he won the January poll.

On Wednesday, Taipei's defence ministry said it had detected 45 Chinese aircraft and six naval vessels operating around Taiwan during the 24-hour period leading up to 6:00 a.m. (2200 GMT).

"26 of the aircraft crossed the median line of the Taiwan Strait," the ministry said in a statement, referring to a line bisecting the 180-kilometre (110-mile) waterway that separates Taiwan from China.

The ministry added that it had "monitored the situation and responded accordingly". 

On Tuesday evening, the ministry said 23 Chinese aircraft -- including fighter jets and drones -- were detected around Taiwan during a two-hour period.

Beijing has in recent years upped military pressure on Taiwan, maintaining a near-daily presence of warplanes, drones and naval vessels around the island.

The largest ever seen around Taiwan was last September, when Beijing sent in 103 warplanes and aircraft -- 40 of which crossed the median line.

Experts say these are "grey zone tactics", which stop short of outright acts of war but serve to exhaust Taipei's military.

Besides deploying a military show of force, China has also sent in coast guard ships and other official fishery vessels around Taiwan's outlying island of Kinmen since February.

The most recent sighting was Tuesday, when five Chinese coast guard ships sailed through Kinmen's "restricted waters" for three hours before leaving, Taiwan's coast guard said. 

Tuesday's sighting was the fifth formation seen in May, which the Taiwanese coast guard said "seriously affect navigation safety and undermine peace and stability across the Taiwan Strait".

"We urge the Chinese side to exercise self-restraint and immediately cease this irrational behaviour," it said.

Lai, like outgoing President Tsai Ing-wen, rejects Beijing's claim over Taiwan.

China has condemned him and his deputy Hsiao Bi-khim -- who was Taiwan's former representative to the United States -- as an "independence duo".