Japan on Tuesday launched a satellite to modernise its military communications and reportedly to better monitor North Korean missile launches.

The Kirameki-2 will enable ground, sea and air units of the military -- known as the Self-Defense Forces -- to communicate directly with each other, a defence ministry official said.

"We'll be able to exchange a large amount of data more quickly," the official told AFP.

"We currently share information with voice and by fax" due to limitations in the speed and capacity of the three civilian satellites the ministry currently uses, he said.

An H-IIA rocket carrying the satellite, which means "sparkle" in English, blasted off from the southern island of Tanegashima at 4:44 pm local time (0744 GMT).

Public broadcaster NHK said the ministry would be able to swiftly share information about ballistic missiles launched by North Korea or videos of Japanese troops deployed overseas.

Japan is on constant alert for moves by North Korea, which conducted two underground nuclear tests and more than 20 missile test-launches last year.

Kirameki-2 is one of three defence communications satellites that will replace the current civilian ones.

The total cost for the three comes to 230 billion yen ($2.48 billion), the ministry said.

The ministry planned to launch Kirameki-1 last year but it is undergoing repairs after being damaged when being transported to a launch site in French Guiana.

Its launch is now scheduled for March 2018 at the earliest.