The Japanese government has said it is "on high alert" and was preparing for a possible North Korean missile launch that could threaten Japan as well as its US and South Korean allies.
Missile interceptors have been deployed in key locations around Tokyo as a precaution.
Japanese Prime Minister Shinzo Abe told reporters that they would take every possible measure to protect their citizens.
On Tuesday, North Korea urged foreign companies and tourists to leave South Korea as the situation on the Korean Peninsula was "inching close to a thermonuclear war."
Through her tears, a North Korean woman told me how she had to escape: risk death while running across the border or die of starvation.
Memories of the Korean war are never far away in South Korea, where residents have grown used to living with the constant threat of war.
North Korea said it will withdraw workers from the Kaesong factory park run jointly with South Korea and suspend all operations there.