The nuclear-armed North says it has completed its first military spy satellite and leader Kim Jong Un has approved final preparations for the launch.
It would be the North's latest step in a series of missile launches and weapons tests in recent months, including one of a new, solid-fuel intercontinental ballistic missile.
Tokyo expects North Korea to fire the rocket carrying its satellite over Japan's southwest island chain as it did in 2016, a defence ministry spokesperson said.
Analysts say the new satellite is part of a surveillance technology programme that includes drones, aimed at improving the ability to strike targets in wartime.
"We will take destructive measures against ballistic and other missiles that are confirmed to land in our territory," Japan's defence ministry said in a statement on Monday.
Japan would use its Standard Missile-3 (SM-3) or Patriot Missile PAC-3 to destroy a North Korean missile, it added.
Any North Korean missile launch would be a serious violation of U.N. Security Council resolutions condemning its nuclear and missile activity, Japanese Prime Minister Fumio Kishida told reporters.
"We strongly urge North Korea to refrain from launching," his office said on Twitter, adding it would co-operate with the US, South Korea and other countries and do all it could to collect and analyse information from any launch.
A US State Department spokesperson said any North Korean launch that uses ballistic missile technology, including that which is used to put a satellite in orbit, would violate multiple UN resolutions.
The US urges North Korea "to refrain from further unlawful activity and calls on Pyongyang to engage in serious and sustained diplomacy," the spokesperson said.
South Korea joined in calling on the reclusive North to scrap its plan, which it described as "illegal."
"If North Korea presses ahead, it will pay the price and suffer," a spokesperson from the South's foreign ministry said in a statement.
Kim Gunn, the South's special envoy for peace and security affairs on the peninsula, held a three-way telephone call with his counterparts from Japan and the United States, the ministry added.
They agreed to work together closely in leading a united response by the international community to Pyongyang's planned move, it said.
But with no serious leverage left on Pyongyang, calls by Tokyo and Seoul to halt the launch will have little effect, said Chad O'Carroll, chief executive of Korea Risk Group, which monitors North Korea.
"Coming amid major US-ROK military drills and in the wake of South Korea's own satellite launch, North Korea is likely to view Seoul's critique as extremely hypocritical."
South Korea's domestically made space rocket delivered a commercial grade satellite into orbit for the first time on Thursday.
North Korea has tried several times to launch "earth observation" satellites, of which two appeared to have been successfully placed in orbit, the latest in 2016.
In May, its leader, Kim, inspected a military satellite facility, the KCNA state news agency said.
In April, Japan sent to the East China Sea a destroyer carrying the SM-3 interceptors that can hit targets in space, and sent ground-based PAC-3 missiles, designed to strike warheads closer to the ground, to the Okinawan islands.
"The government recognises that there is a possibility that the satellite may pass through our country's territory," Hirokazu Matsuno, the chief cabinet secretary, told a regular briefing after the North informed the Japanese coast guard of the plan.
North Korean state media have criticised plans by Japan, South Korea and the United States to share real-time data on its missile launches, characterising the three as discussing "sinister measures" to tighten military co-operation.
