Beijing insists self-ruled Taiwan is part of its territory and opposes any international recognition of the island and its claim to be a sovereign nation.

To press its claims, China deploys fighter jets, drones and warships around Taiwan on a near-daily basis, with the number of sorties increasing in recent years.

In the 24 hours to 6:00 am on Friday (2200 GMT Thursday), Taiwan's defence ministry said it had detected 33 Chinese aircraft and eight navy vessels in its airspace and waters.

That included 19 aircraft that took part in China's "joint combat readiness patrol" on Thursday evening and was the highest number in more than three weeks, according to an AFP tally of figures released daily by the ministry.

Taiwan also spotted a balloon -- the fourth since Sunday -- about 172 kilometres (107 miles) west of the island.

"It can't be ruled out that there will be a relatively large-scale military exercise in response to Lai's visit," Su Tzu-yun, a military expert at Taiwan's Institute for National Defense and Security Research, told AFP.

- 'Old friends' -

Lai, an outspoken defender of Taiwan's sovereignty and whom China calls a "separatist", departs Saturday on his first overseas trip since taking office in May.

He will stop briefly in Hawaii and the US territory of Guam to meet "old friends", as he visits Taiwan's three remaining allies in the Pacific.

Taiwanese government officials have previously stopped over on US soil during visits to the Pacific or Latin America, angering China, which has sometimes responded with military drills around the island.

China has reacted furiously to Lai's planned trip, with a spokesperson for the defence ministry vowing Thursday to "resolutely crush" any attempts for Taiwan independence.

Asked whether China's military would take countermeasures over Lai's Pacific tour, Wu Qian said: "We firmly oppose official interaction with China's Taiwan region in any form."

China has staged two large-scale military drills around Taiwan since Lai took office and verbally attacked him at every turn over his statements and speeches.

Lin Ying-yu, a military expert at Tamkang University, said China's response would be determined by Lai's remarks during the trip.

"China may carry out military exercises, but they may not be large ones. It will depend on what President Lai says," Lin told AFP, adding the current weather was "not very good" for drills.

- 'Legitimacy' -

The South Pacific was once seen as a bastion of support for Taiwan's claim to statehood, but China has methodically whittled this down.

In the past five years, Solomon Islands, Kiribati and Nauru have all been persuaded to switch diplomatic recognition from Taipei to Beijing.

The Marshall Islands, Tuvalu and Palau are now the only Pacific island nations among Taiwan's 12 remaining diplomatic allies.

Beijing's efforts to woo Taiwan's allies and expand its influence in the region have alarmed the United States, Australia and New Zealand.

Switching recognition to China "opened the door to much deeper engagement between Beijing and those countries," said Mark Harrison, a senior lecturer in Chinese studies at the University of Tasmania.

Lai's trip was a rare opportunity for the president to represent Taiwan abroad and bolster its claim to statehood.

"Even though they kind of look theatrical and performative, (these trips) actually give Taiwan a genuine voice in the international system," Harrision told AFP.

"They confer legitimacy, they confer the appearance of sovereignty and, with the international system as it is, the appearance of sovereignty is also sovereignty."