Dubbed "United Sharp Sword", the three-day operation -- which state media said includes rehearsing an encirclement of Taiwan -- will run until Monday, the People's Liberation Army's (PLA) Eastern Theatre Command said in a statement.
Taiwanese President Tsai Ing-wen immediately denounced the drills, pledging to work with "the US and other like-minded countries" in the face of "continued authoritarian expansionism".
China's war games will send planes, ships and personnel into "the maritime areas and air space of the Taiwan Strait, off the northern and southern coasts of the island, and to the island's east", said Shi Yin, a PLA spokesman.
A later report from state broadcaster CCTV said: "The task force will simultaneously organise patrols and advances around Taiwan island, shaping an all-round encirclement and deterrence posture."
The report went on to detail the type of weaponry China was putting through its paces, including "long-range rocket artillery, naval destroyers, missile boats, air force fighters, bombers, jammers and refuellers".
Taiwan's defence ministry released a video showing soldiers loading anti-aircraft missile launchers, fighter jets taking off, and other military preparedness exercises.
The footage included surveillance of China's Shandong aircraft carrier, which sailed through waters south of Taiwan earlier this week.
The 75-second clip, which included English subtitles, ended with a caption saying: "We seek neither escalation nor conflict, but we remain steadfast, rational, and serious to react and defend our territory and sovereignty."
Exercises on Monday will include live-fire drills off the coast of China's Fujian province, which faces Taiwan, the local maritime authority said.
The manoeuvres come after a meeting between Tsai and US House Speaker Kevin McCarthy in California.
China views democratic, self-ruled Taiwan as part of its territory and has vowed to seize it one day, by force if necessary.
"These operations serve as a stern warning against the collusion between separatist forces seeking 'Taiwan independence' and external forces and against their provocative activities," the PLA's Shi said.
"The operations are necessary for safeguarding China's national sovereignty and territorial integrity."
Taiwan's defence ministry said eight Chinese warships and 42 fighter jets were detected around the island on Saturday.
The ministry expressed "solemn condemnation of such irrational actions", adding the detections included 29 jets that crossed into Taiwan's southwestern air defence identification zone (ADIZ), the highest number in a single day this year, according to data collected by AFP.
China was using Tsai's US visit as an "excuse to conduct military exercises, which has seriously undermined peace, stability and security in the region", the Taiwanese ministry said.
The drills also follow the departure from Beijing of French President Emmanuel Macron and EU chief Ursula von der Leyen, who were in China to urge Xi Jinping to help bring an end to the war in Ukraine.
'We will never yield'
China deployed warships, missiles and fighter jets around Taiwan last August in its largest show of force in years, following a trip to the island by McCarthy's predecessor, Nancy Pelosi.
McCarthy, who is second in line to the US presidency, had originally planned to go to Taiwan himself.
The decision to meet in California instead was viewed as a compromise that would underscore support for Taiwan but avoid inflaming tensions with Beijing.
There were no immediate signs on Saturday of heightened military activity on Pingtan, a southeastern Chinese island that is the closest point on the mainland to Taiwan.
A handful of cargo ships cruised through the waters near the coastline, while tourists in sunglasses and baseball caps snapped selfies on viewing platforms.
But Fujian's provincial maritime authority has warned vessels not to enter waters near the live-fire drills on Monday.
Tsai returned to Taiwan on Friday after visiting her island's dwindling band of official diplomatic allies in Latin America, with two US stopovers that included meetings with McCarthy and other lawmakers.
Hours before Tsai met McCarthy on Wednesday, China sent its Shandong aircraft carrier through Taiwan's southeastern waters on its way to the western Pacific.
Beijing said Friday that "Taiwan is an inseparable part of China", after repeatedly warning against the Tsai-McCarthy meeting.
"China's sovereignty and territorial integrity will never be divided," foreign ministry spokeswoman Mao Ning said at a regular news briefing.
"The future of Taiwan lies in reunification with the motherland."
Chinese military commentator Song Zhongping said the exercises were intended to demonstrate that the Chinese army will be ready if "provocation intensifies" to "solve the Taiwan issue once and for all".