TAIPEI, Dec 7 (Reuters) - Taiwan reported rare nighttime Chinese military activity around the island on Thursday, including aircraft crossing the sensitive median line of the Taiwan Strait, as Beijing continues such missions ahead of Taiwan's January election.

Democratically governed Taiwan, which China claims as its own territory, has complained for the past four years of regular Chinese military patrols and drills near the island.

Taiwan holds presidential and parliamentary polls on Jan. 13 and campaigning has kicked into high gear.

Relations with China are a major point of contention.

Taiwan's defence ministry said that starting around 7.30 pm (1130 GMT) on Thursday evening it had detected Su-30, J-10 and J-11 fighters as well as nuclear capable H-6 bombers and early warning aircraft operating off northern and central Taiwan and to the island's southwest.

Thirteen of those aircraft crossed the Taiwan Strait's median line, or areas close by, working with Chinese warships to carry out "joint combat readiness patrols", the ministry added.

The strait's median line once served as an unofficial barrier between the two sides, but Chinese planes now regularly fly over it.

Taiwan sent its own forces to monitor, the ministry said.

Over the past month, Taiwan has reported at least four other similar large-scale sorties by China's air force, which Beijing has not commented on, though those took place during the day.

China says its activities near Taiwan are aimed at preventing "collusion" between Taiwan separatists and the United States, and protecting China's territorial integrity.

Taiwan's government, which has repeatedly offered talks with China, rejects Beijing's sovereignty claims and says only the island's people can decide their future.

The ruling Democratic Progressive Party's Lai Ching-te, whom Beijing has denounced as a separatist, is the frontrunner to be Taiwan's next president, according to opinion polls.

Taiwan's main opposition party, the Kuomintang, traditionally supports close ties with Beijing, and has pledged to reopen dialogue with China if it wins the election.

Photo from Reuters