Taiwan again reported Chinese military activity around the island on Wednesday, with 11 aircraft crossing the sensitive median line of the Taiwan Strait as the island's election campaign kicked into high gear.

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, as Beijing seeks to pressure Taipei over its sovereignty claims.

Taiwan holds presidential and parliamentary polls on Jan. 13 and candidates have to register with the election commission this week in order to take part.

The ruling Democratic Progressive Party (DPP), which Beijing views as separatists, registered its presidential ticket on Tuesday, though the opposition is mired in disagreement about a potential joint bid.

Taiwan's defence ministry said that starting early Wednesday afternoon it had detected J-10 and J-16 fighters as well as H-6 bombers and early warning aircraft carrying out overseas missions.

Eleven of those aircraft crossed the Taiwan Strait's median line flying in airspace to the centre and southwest of the island, working with Chinese warships to carry out "joint combat readiness patrols", the ministry added.

The strait's median line had previously served as an unofficial barrier between the two sides and which Chinese planes now regularly fly over.

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

China's defence ministry did not answer calls seeking comment. China says its activities near Taiwan are aimed at preventing "collusion" between Taiwan separatists and the United States and to protect 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.

Taiwan's main opposition party, the Kuomintang, traditionally supports close ties with Beijing, and has pledged to re-open dialogue with China should it win the election.