China has launched the first of its four-day military training drills in response to Taiwan's hosting of a top US politician.
There are concerns China will go further than ever before - with reports from state media suggesting it will fire missiles over the top of Taiwan, a self-governing island of 23 million people.
Taiwan only has a small military and relies on the United States for weapons and support.
The island nation is in China's firing line after hosting US House Speaker Nancy Pelosi - a fervent critic of China's human rights record.
Pelosi says her trip was about strengthening "democracy" - but was careful to steer away from any use of the word "independence".
"[We] don't want anything to happen to Taiwan by force," she said.
"One of the biggest forces of strength is democracy."
That wasn't enough to avoid raising the ire of China anyway, which has labelled her trip a "violation" and in response, announced days of live-fire military drills.
"China has repeatedly expressed its opposition to Pelosi's Taiwan visit," said China's Foreign Ministry spokesperson Hua Chunying.
"The US and Taiwan separatist forces seem not to have heard. In this case, China can only speak to them in the language that they can understand."
China is conducting drills across six different sites encircling Taiwan, deliberately blocking commercial shipping lanes and air space.
"During this actual combat exercises, six major areas around the island were selected and during this period all ships and aircraft should not enter the relevant sea areas and airspace," Chinese state broadcaster CCTV said after announcing that the drills began at 12pm (local time).
Taiwan's defence ministry said its armed forced would operate as usual.
"We seek no escalation, but we don't stand down when it comes to our security and sovereignty," it said.
"The United States will not seek, and does not want a crisis here, but we are prepared to manage what Beijing chooses to do," said White House spokesperson Karine Jean-Pierre.
The wider region is ready to respond, with Taiwan's military raising its alert level while US naval warships sit to the east of Taiwan, and American troops undertake training further south in Indonesia.