TAIPEI - Taiwan said yesterday that its military planes have made about 30 flights into a part of mainland China's newly declared air defence zone which overlaps a similar Taiwanese zone.

The announcement came as South Korean officials said Seoul is likely to expand its ADIZ soon in response to China's move, and the extension would cover the previously overlooked submerged reef of Ieo and the islands of Marado and Hongdo, all of which belong to the country.

Taiwanese Defence Minister Yen Ming, answering questions in Parliament yesterday, said the Taiwanese planes made the entry in the past week or so.

There was no mention that China scrambled planes in response, but Mr Yen said Taiwan's air force would send planes to shadow any Chinese military aircraft that enters the overlapping area, Agence France-Presse reported.

Japan and South Korea both said last week that they had flown into the Chinese air zone without notifying Beijing, after United States B-52 bombers did likewise.

China's unilateral announcement on Nov 23 of an Air Defence Identification Zone (ADIZ) in the East China Sea has raised anxiety in the US, Japan and South Korea as well as Taiwan.

Beijing demands that all aircraft submit flight plans when traversing the zone, which covers islands disputed with Tokyo and also claimed by Taipei.

Mr Yen earlier told reporters that Taiwan's ADIZ has not changed and "our training operations and patrols" within the area remain normal, reported Taiwan's Central News Agency.

But he told Parliament that the air force would refrain from conducting bombing exercises in the overlapping area, to avoid fuelling tensions.

Last Friday, the Ma Ying-jeou administration, which has been pushing for detente with the mainland since 2008, launched a belated protest about the zone following mounting pressure from the opposition.

Taiwan's Parliament has passed a bipartisan resolution urging the government not to present flight plans to Beijing even though the island's Civil Aeronautics Administration agreed last week to do so.

In Seoul, officials said they will inform China, Japan and the US of the decision rather than negotiate with them on the expansion. The Chosun Ilbo quoted a Defence Ministry official as saying this, following a meeting held on Sunday chaired by presidential security adviser Kim Jang Soo.

The government was expected to finalise the boundaries of its new ADIZ this week after consultations with lawmakers of the ruling Saenuri Party, reported China's Xinhua news agency.

Both the Chinese and Japanese ADIZs include Ieo, whose surrounding waters are controlled by South Korea, said Chosun.

Officials are instructed to make the new boundaries coincide with the Korea Flight Information Region, which was demarcated to ensure smooth air traffic flow and already includes a large part of Japan's ADIZ as well as Ieo, Chosun said. Marked out in 1951 by the US Air Force, South Korea's current ADIZ does not cover many remote spots, reported South Korea's Yonhap News Agency.