North Korea is preparing to test-fire short-range missiles in the Yellow Sea, one day after it staged a nuclear test, South Korea's Yonhap news agency said Tuesday.

"North Korea has declared an off-limits area for vessels in the Yellow Sea off Jungsan county in South Pyongan province," it quoted a Seoul government source as saying.

"The North is likely to fire short-range missiles today or tomorrow."

Jungsan is about 40 km (25 miles) west of Pyongyang.

The Joint Chiefs of Staff said it could not comment on intelligence matters.

The North Monday staged its second underground nuclear test, with an explosive force much larger than the first in October 2006.

It also fired three short-range ground-to-air missiles from locations near its east coast, Seoul's military said.

Several times in recent years, the North has test-fired ground-to-ship or ship-to-ship missiles in either the Yellow Sea or the Sea of Japan (East Sea).

The launches are often staged to coincide with periods of regional tension.

Yonhap said the North is preparing to launch ground-to-ship missiles with a range of 160 km (100 miles), which use technology based on China's Silkworm missiles.

The South summoned an emergency meeting of top military commanders to review its defence posture, a Joint Chiefs of Staff spokesman said.

The meeting would stress the need to heighten vigilance against the North's "militarily provocative acts," the spokesman told AFP.