The short message from Taiwan's defence ministry was sent after 3 p.m. local time to mobile phone users in Taiwan. The "presidential alert" gave no additional details.

Chinese state news agency Xinhua said China had launched "a new astronomical satellite" called the Einstein Probe from the southwestern province of Sichuan.

China had not previously announced the satellite launch and did not offer any details on its flight plan.

The alert came as Taiwan's Foreign Minister Joseph Wu was giving a press conference ahead of the Jan. 13 presidential and parliamentary elections.

"This is something we have been coping with for a long time. For the Taiwan government, our military stands ready to deal with any kind of emergency," Wu said, addressing a question on the satellite and possible Chinese military provocations.

Wu told reporters a "satellite carried by a rocket" had flown over the southern part of Taiwan, but said he had no further information.

(Reporting by James Pomfret and Sarah Wu; Editing by Jacqueline Wong and Ed Osmond)