Japan today placed its ballistic missile defences on alert and warned that it would shoot down any projectile threatening its territory.

This was after North Korea notified it of a satellite launch between May 31 and June 11.

The nuclear-armed East Asian state says it has completed its first military spy satellite, and leader Kim Jong Un has approved final preparations for the launch.

"The government recognises there is a possibility the satellite may pass through our country's territory," said Japan's chief cabinet secretary, Hirokazu Matsuno.

He told this at a briefing after North Korea informed the Japanese coast guard of the planned launch.

The Japanese defence ministry order saw its first response to a North Korean space launch since 2016.

This comes after Japan dispatched to the East China Sea a destroyer carrying Standard Missile-3 (SM-3) interceptors that can hit targets in space in April.

It also sent ground-based PAC-3 missiles to the Okinawan islands to strike warheads closer to the ground.

A defence ministry spokesperson said that Japan expects North Korea to fire the rocket carrying its satellite over Japan’s southwest island chain as it did in 2016.

North Korean state media has criticised plans by its rivals, South Korea, the United States and Japan, to share real-time data on its missile launches.

It describes the three as discussing "sinister measures" for tightening military cooperation.

Analysts say the satellite is part of a surveillance technology programme that includes drones, meant to improve its ability to strike targets in the event of war.

Kim in May inspected a military satellite facility, the North's KCNA state news agency reported.

North Korea has conducted a series of missile launches and weapons tests in recent months, including a new, solid-fuel intercontinental ballistic missile.

Japanese Prime Minister Fumio Kishida said any North Korean missile launch would seriously violate UN Security Council resolutions condemning its nuclear and missile activity.

"We strongly urge North Korea to refrain from launching," his office posted on Twitter.

His office also said it would cooperate with its US ally, South Korea and other countries, and do all it could to collect and analyse information from any launch.

- Reuters