The country already has one of the largest armed forces in the world.
The leader made the remarks during a tour of the country’s missile facilities on Sunday, before a meeting between leaders of the US, Japan and South Korea.
He said his country needed to “drastically” increase its production of missiles and launchers.
Last week, he said he wanted the armed forces to be "perfectly ready" for a potential conflict.
North Korea possesses about 6,000 rocket launch systems and guns, the US defence think tank Rand said. Other estimates put the total as high as 10,000.
A 2020 Rand study said the North could inflict 10,000 casualties every hour during an artillery bombardment on South Korea.
Mr Kim “set forth an important goal to drastically boost the existing missile production capacity", adding that he called on workers to step up production to aid in front-line defences and strategic weapons systems, the state-run Korean Central News Agency reported.
Mr Kim reportedly called for the country to build more mobile missile launcher systems, including nuclear-capable systems, which are harder to locate after launching their weapons.
Japanese Prime Minister Fumio Kishida, South Korean President Yoon Suk Yeol and US President Joe Biden plan to discuss how to respond to the North Korean nuclear and missile threats when they meet at Camp David on Friday, Kim Tae-hyo, a South Korean National Security Council official, said on Sunday.
The three countries have increased information sharing on North Korean missile launches to better track rockets and are looking to boost joint military drills among the three, Kyodo News of Japan reported last week.
The US and Japan are expected to announce an agreement to jointly develop missile interceptors for hypersonic weapons during the meeting, the Yomiuri newspaper reported, quoting government officials.