President Donald Trump promised on Japanese Prime Minister Shinzo Abe's behalf that Japan would shoot down North Korean missile tests that overfly his country.

Japan has several missile-defense platforms that could knock down a North Korean missile test, but it's easier said than done.

Abe is hawkish for a Japanese leader, but Trump has consistently overestimated the efficacy of missile defense and taken the most aggressive line towards North Korea.

President Donald Trump sits down to dinner with Japanese Prime Minister Shinzo Abe. AP Photo/Susan Walsh President Donald Trump said Japan will buy more US military equipment and take down North Korean missile tests that overfly the country.

"He will shoot them out of the sky when he contemplates the purchase of a lot of military equipment from the United States," Trump said alongside Japanese Prime Minister Shinzo Abe at a news conference.

"The Prime Minister of Japan is going to be purchasing massive amounts of military equipment, as he should," Trump said.

Trump had been questioning for some time Japan's handling of North Korean missile tests and asked why a nation of samurai warriors would not shoot down missiles overhead, according to sources that spoke to the Japan Times.

North Korea has tested long-range missiles by overflying Japan and recently tested what it called a hydrogen bomb.

Japan operates US-built missile defense systems both on land and aboard its navy's ships, but the intercontinental-range ballistic missiles (ICBM) tested by North Korea fly with such velocity that intercepting them remains a challenge, even for the most advanced platforms.

Japan has not previously attempted to shoot down North Korean missile overflights, nor has the US. With limited warning beforehand and missile defense not a foolproof solution, experts remain split on the wisdom of attempting to shoot down test launches.

While destroying a North Korean missile test in flight would rob Pyongyang of valuable test flight data, if the intercept attempt failed, it would erode the credibility of US and allied defenses.

Members of the Japan Self-Defence Forces stand guard near Patriot Advanced Capability-3 (PAC-3) land-to-air missiles, deployed at the Defense Ministry in Tokyo, Japan, December 7, 2012. REUTERS/Issei Kato

Japan recently reelected Abe, the country's most militarily assertive leader in decades, but Trump's hawkishness on North Korea surpasses Abe's and perhaps even the capabilities of his own military.

Trump previously said that US missile defenses can knock down North Korean missiles "97% of the time," despite the fact that only in watered-down test settings can missile interceptors achieve that degree of success.

In war fighting conditions, experts assess that the US, or allies using US-designed systems, would struggle to down ICBMs, and may prove essentially ineffective against salvos of multiple missiles.