Japan has only about 60% of missile stockpiles deemed sufficient to intercept enemies' ballistic missiles, the Defense Ministry has said, in a call for urgent replenishment amid military threats from North Korea and China.

In a rare move for the ministry, an official revealed the estimated ammunition sufficiency rate to reporters Friday, as Prime Minister Fumio Kishida aims to update the government's long-term security and diplomacy policy guideline by the end of this year and to secure a larger defense budget to strengthen the country's defense capabilities.

The National Security Strategy, along with two other key documents on the defense buildup, is expected to be revised for the first time since it was adopted in 2013, at a time when China is intensifying its maritime assertiveness in the Indo-Pacific region and North Korea's ballistic missile testing has gathered pace.

China is also believed to have about 1,900 medium-range ballistic missiles and 300 medium-range cruise missiles capable of reaching Japan, according to a U.S. Defense Department analysis.

The current situation "should be improved as soon as possible," since Japan might not be fully prepared if it comes under attack, the official said, pointing to soaring costs for anti-ballistic missiles per unit due to cutting-edge technologies used for them as a cause of the insufficient stockpiles.

Japan's missile defense consists of two layers. Maritime Self-Defense Force Aegis destroyers equipped with Standard Missile-3 interceptors are tasked with hitting incoming missiles in the outer atmosphere. If the SM-3s fail to intercept them, the Air Self-Defense Force's ground-based Patriot Advanced Capability-3 interceptors will counter the attack in the lower tier.