China has fired missiles near Taiwan as part of huge military drills following a visit by senior US politician Nancy Pelosi to the island.
Taiwan said China launched 11 ballistic missiles into waters around Taiwan's north-east and south-west coasts.
Japan said five Chinese missiles landed in its waters as well, calling for an "immediate stop" to the exercises.
China saw the visit, by the US house speaker Pelosi, as a challenge to its claims of sovereignty over Taiwan.
It sees Taiwan as a breakaway province that will eventually be brought under its control - by force if necessary.
The US, for its part, does not officially recognise Taiwan, which has for all practical purposes been independent since 1950. However, Washington maintains a strong relationship with the island - which includes selling weapons for Taiwan to defend itself.
"The exercises focus on key training sessions including joint blockade, sea target assault, strike on ground targets, airspace control operation," the Chinese military's Eastern Theater Command said in a statement.
Pelosi's brief visit to Taiwan on Wednesday fuelled tensions, with Chinese Foreign Minister Wang Yi describing it as "manic, irresponsible and irrational". She is the most senior US politician to visit the island in 25 years.
China responded by conducting an unprecedented launch of ballistic missiles and the military drills just off the Taiwanese coast.
Taiwan's defence ministry said it had activated its defence systems and was monitoring the situation.
Taiwan's ministry of foreign affairs accused China of "following the example of North Korea in wilfully test-firing missiles into waters near other countries".
North Korea - a strong ally of China's - has been accused of igniting tensions in the region by repeatedly launching missile tests in recent months.
On Thursday, Japan voiced its strong protest over the Chinese missile launches.
"We strongly condemn the act as it is a serious issue concerning Japan's security and the safety of Japanese people," Japanese Defence Minister Nobuo Kishi said.
China's missile launches are causing disruption to shipping lanes and flights to and from Taiwan.
Ships have been forced to re-route, with days-long disruptions expected to have an impact on supply chains with delays to global shipping.
More than 50 international flights from Taiwan's Taoyuan International Airport have been cancelled.
- BBC