The first drills began at 12pm local time (4am GMT) in the seas around Taiwan, with some taking place within 12 miles of the island.
The Taiwanese President Tsai Ing-wen has said the island faces “deliberately heightened military threats”.
Ms Pelosi made a brief but controversial trip to Taiwan, sparking fury in Beijing as China views the island as its territory.
China has responded with some of the biggest military drills it has ever carried out around Taiwan, with the exercises taking place in busy waterways and with long-range live ammunition shooting.
Beijing has also blocked some trade with the island, reported the BBC.
The Taiwanese Government said on Wednesday that it had scrambled jets to warn off Chinese warplanes and had fired flares to discourage drone attacks.
Their defence ministry also said they had experienced cyber attacks, which had targeted other government websites as well.
US National Security Advisor Jake Sullivan warned China that the drills were irresponsible and could spiral out of control.
In an interview with National Public Radio he said he hoped Beijing would avoid “escalation that could lead to a mistake or miscalculation”.
READ MORE: GB News: Pelosi torn apart over ‘foolish’ Taiwan visit amid war fears
As Speaker of the House, Ms Pelosi is the most senior US Government Representative to visit Taiwan in 25 years.
During the trip Ms Pelosi assured President Tsai that the US would not abandon the island.
Beijing accused her of “violating China’s sovereignty under the guise of so-called democracy”, as Chinese Foreign Minister Wang Yi said: “Those who play with fire will not come to a good end and those who offend China will be punished.”
