Taiwan authorities said on Tuesday afternoon that a Chinese satellite had flown over southern Taiwan’s airspace.
Mobile phone users across Taiwan received an “air raid alert” warning them to “be aware for your safety”.
The satellite was launched off the Xichang Satellite Launch Centre in China’s Sichuan province at 15:03 local time, Taiwan’s defence ministry said.
Chinese broadcaster CCTV confirmed a satellite named Einstein Probe had been launched from the centre.
It added that the launch mission was a “complete success”.
Taiwan said its ministry is looking into the trajectory of the satellite to “appropriately alert and respond” to the situation.
Taiwanese media say this is the first time its government has flashed an islandwide alert of this nature.
The incident comes days before pivotal presidential and legislative elections in Taiwan, which analysts have said will shape the trajectory of ties between Beijing and Washington.
According to the European Space Agency, the Einstein Probe is a partnership between the agency, the Chinese Academy of Sciences and the Max Planck Institute for Extraterrestrial Physics. The mission’s theme is to “monitor the universe in X-ray light”.