South Korea has expanded its air defence zone after the Chinese controversially decided to push out theirs, with the two now overlapping over a disputed reef.

The new zone covers a submerged rock called Ideo, where the South Koreans have a research station. Ideo is claimed by the Chinese, and the new zone overlaps with China's own zone at other points.

Defence Ministry spokesman Kim Min-seok said that Seoul would talk with the governments of neighbouring countries to avoid accidental clashes in overlapping areas.

"We believe this will not significantly impact our relationships with China and with Japan as we try to work for peace and cooperation in Northeast Asia," defence ministry head of policy Jang Hyuk told a briefing.

He said that the government had briefed neighbours on its plans before the announcement.

South Korea, Japan and the United States all objected to China's unilateral decision last week to expand its air defence zone to encompass the disputed islands of Diaoyu or Senkaku in the East China Sea. Both China and Japan claim ownership of the islands.

China says that all planes flying through the zone must identify themselves and follow its rules.

Since then, South Korea, the US, and Japan have all flown reconnaissance flights in the area without notifying the Chinese.

South Korean airliners have also been advised to ignore the zone.

The US - which described China's move as causing "significant apprehension in the region" - said it supported Seoul's action.

"The United States has been and will remain in close consultation with our allies and partners in the region to ensure their actions contribute to greater stability, predictability, and consistency with international practices," State Department spokeswoman Jen Psaki said.