China began its largest military exercise around the Taiwan Strait following the departure of US House Speaker Nancy Pelosi.
Live firing exercises began at 12.00 local time in several areas within 12 miles of the island.
Meanwhile, China said the drills would be held in busy waterways and would include long-range live ammunition firing.
Nancy Pelosi, who has made her highest-level visit in 25 years to Taiwan, has angered China, which has previously repeatedly warned against her coming to the island.
Beijing claims Taiwan as its own and does not rule out the use of force to control the island.
In response to China's actions, Taipei said the exercise violated United Nations (UN) rules, invaded Taiwan's territorial space and was a direct challenge to freedom of air and sea navigation.
The Democratic Progressive Party (DPP) said China was conducting exercises on the busiest international waterways and airlines and that it was 'irresponsible, illegal behaviour.'
Taiwan's cabinet spokesman, who expressed serious condemnation of the exercise, also said the websites of the defense ministry, the foreign ministry and the president's office had been attacked by hackers.
Although the tension appears to have subsided, it could rekindle the risk if the United States responds to this provocation.
