• China sees Taiwan as a break-away province that will eventually be brought under its control - by force if necessary.
• The US, for its part, does not officially recognise Taiwan. It does, however, maintain a strong relationship with the island - which includes selling weapons for Taiwan to defend itself.
Taiwan has accused China of imitating North Korea by firing missiles into the sea around the island.
China launched 11 ballistic missiles into waters around Taiwan's north-east and south-west coasts, Taiwan said.
The launches, just miles from the coast, followed US House Speaker Nancy Pelosi's visit to Taiwan on Wednesday.
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.
China sees Taiwan as a break-away province that will eventually be brought under its control - by force if necessary.
The US, for its part, does not officially recognise Taiwan. It does, however, maintain a strong relationship with the island - which includes selling weapons for Taiwan to defend itself.
Ms Pelosi's visit to the island therefore fuelled tensions, with China accusing the US of behaving irresponsibly.
A day later, China began an unprecedented launch of ballistic missiles and military drills just off the Taiwanese coast.
In response, Taiwan's defence ministry said it had activated its defence systems and was monitoring the situation.
Taiwan's ministry of foreign affairs, meanwhile, accused China of "following the example of North Korea in wilfully test-firing missiles into waters near other countries".
China also launched live fire drills, which are set to end on Sunday.
China's missile launches and drills are taking place in some of the world's busiest waterways, 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.
In wake of the increased tensions, the US navy said a naval carrier - the USS Ronald Reagan - was heading towards part of the ocean that includes waters south-east of Taiwan.
"USS Ronald Reagan and her strike group are under way in the Philippine Sea continuing normal, scheduled operations as part of her routine patrol in support of a free and open Indo-Pacific," a navy spokesperson said on Thursday.
A US aircraft that can track ballistic missiles in flight has also taken off from Japan and is heading towards Taiwan.