Taiwan on Monday rejected China's call for the opening of restricted air space over the Taiwan Strait to help meet rising passenger demand between the island and the mainland.

Flights currently have to make a detour around the restricted air space -- "the median line" -- between China and Taiwan.

Wang Yi, chief of the Taiwan Affairs Office of the Chinese State Council, last week said an agreement for 270 flights a week was not enough to cope with rising passenger numbers.

He recommended flight numbers be more than doubled and urged Taiwanese authorities to allow passenger aircraft to cross the median line.

But Taiwan's defence ministry dismissed the proposal on Monday, saying "the median line is extremely important to Taiwan's air security."

Taiwan's military said the restriction gives its air force more time and space to react to any Chinese attack.

"Before the Chinese communists publicly renounce their desires of invading Taiwan by force and re-adjust their military deployment targeting the island, the current flight routes should stay unchanged," the ministry said in a statement.

Although the island has governed itself since 1949, China has threatened to invade Taiwan should the island formally declare independence.

The People's Liberation Army is pointing over 1,000 ballistic missiles across the strait, according to Taiwan's defence ministry.

The defence ministry's statement came after Taiwanese President Ma Ying-jeou turned down the proposal last week, local media reported.

Ties between the two sides have, however, improved dramatically since Ma, of the China-friendly Kuomintang, came to power last year promising to promote reconciliation and trade links with the mainland.

In recent months Taipei and Beijing have signed a raft of agreements that have led to regular direct flights and greater cooperation.

Ma's predecessor, Chen Shui-ban, often antagonised Beijing with pro-independence rhetoric.