North Korea says leader Kim Jong Un observed the first test-firings of missiles from a recently launched destroyer and called for speeding efforts to boost his navy’s nuclear attack capabilities.

The 5,000-tonne warship is equipped with the "most powerful weapons" and built "within 400-odd days perfectly with our own strength and technology," Jo Chun Ryong, a secretary in the ruling Workers' Party, was quoted as saying.

Kim, in a speech from the launch reported by KCNA, said the warship would be handed over to the navy and go into service early next year