The Defense Minister also ordered the deployment of destroyers equipped with SM-3 ship-to-air missiles in Japanese coastal waters.
Japan has activated missile interceptors and is preparing to shoot down fragments of a North Korean satellite that could fall into Japanese territory.
Defense Minister Yasukazu Hamada on Saturday instructed troops to ready PAC-3 surface-to-air missiles in southwest Japan, including Okinawa and nearby islands, in an area believed to be under a flight path of a North Korean missile that the satellite will carry.
He also ordered the deployment of destroyers equipped with SM-3 ship-to-air missiles to coastal waters, according to a statement from the ministry.
“We are making the necessary preparations because of the possibility of issuing an order to destroy ballistic missiles and other objects,” it said.
Hamada instructed troops to “take whatever measures are necessary to limit damage in the event of a ballistic missile strike”.
An order to fire missiles must be approved by the prime minister.
North Korean leader Kim Jong-un said earlier this week that the first military spy satellite will be launched at an undetermined date.
In 2012 and 2016, North Korea tested ballistic missiles that Pyongyang called satellite launches. Both missiles flew over the Okinawa region.
‘Invasion Rehearsal’
North Korea has fired about 100 missiles since early last year and said it was responding to joint US and South Korean military maneuvers it calls an invasion rehearsal. Several of the missiles flew over Japan or landed off the northern Japanese coast.
Last week, North Korea tested its first solid-fuel intercontinental ballistic missile.
North Korea is expected to conduct more weapons tests as the United States and South Korea continue their joint air exercise next week.
On Tuesday, G7 foreign ministers in Japan demanded that North Korea abandon further ballistic missile tests after a spate of launches this year. The group of rich countries also warned Pyongyang against conducting an expected nuclear weapons test, saying there would be a “robust” response if it failed to comply.