Taiwan's air force scrambled into action on Sunday after spotting 10 Chinese warplanes crossing the sensitive median line of the Taiwan Strait, as the island's defence ministry said four Chinese warships also carried out combat patrols.

This is the second time in less than a week that Taiwan has reported renewed Chinese military activity, after 37 Chinese military aircraft on Thursday flew into the island's air defence zone, some of which then flew into the western Pacific.

China, which views democratically governed Taiwan as its own territory, has over the past three years regularly flown its air force into the skies near the island, though not into Taiwan's territorial air space.

In a short statement, Taiwan's defence ministry said that as of 2pm (0600GMT) on Sunday it had detected 24 Chinese air force planes, including J-10, J-11, J-16 and Su-30 fighters, as well as H-6 bombers.

It did not say exactly where those aircraft flew, but did say 10 had crossed the median line of the Taiwan Strait which separates the two sides and had previously served as an unofficial barrier, though China says it does not recognise that and has been routinely crossing it since last year.

Four Chinese naval ships were also engaged in "joint combat readiness patrols", the ministry added, without giving details.

Taiwan sent up its own fighters and deployed ships and land-based missile systems to keep watch, it said, using typical wording for how it responds to such Chinese activities.

There was no immediate response from China's military.

In April, China held war games around Taiwan following a trip to the United States by Taiwan President Tsai Ing-wen.

Taiwan's government rejects China's sovereignty claims and says only the island's people can decide their future.