South Korea has raised its military watch alert to "vital threat" and Japan is on full alert ahead of an expected North Korean missile launch, as United Nations chief Ban Ki-moon warned the Korean Peninsula may be slipping out of control.
South Korean intelligence says the North had prepared two mid-range missiles for imminent launch from its east coast, despite warnings from ally China to avoid provocative moves at a time of soaring military tensions.
Last week, North Korea told foreign diplomats in Pyongyang they had until yesterday to consider evacuation, fuelling speculation that a launch was planned between yesterday and the April 15 birthday celebrations for founding leader Kim Il Sung.
The North has again warned that the region faced "thermonuclear" war and advised foreigners to consider leaving South Korea.
The South Korea-US Combined Forces Command raised its "Watchcon" status from 3 to 2 reflecting signs of a "vital threat".
Yonhap news agency quoted a government source as saying Pyongyang might be preparing "multiple" launches, after other launch vehicles were reportedly detected carrying shorter-range Scud and Rodong missiles.
Japan's Defence Minister Itsunori Onodera said: "We have been on full alert since we deployed military units, and so we will maintain this sense of vigilance."
As global concerns increase, Ban said: "The current level of tension is very dangerous, a small incident caused by miscalculation or misjudgment may create an uncontrollable situation."