North Korea staged a display of multiple rocket launchers outside the Workers' Party congress venue in Pyongyang, state media said.
Leader Kim Jong Un attended the event on Wednesday and was shown standing beside one of the vehicles as it drove around the site in Pyongyang.
KCNA said Kim told officials the congress would outline plans to strengthen self-reliant defence capabilities.
State television also showed Kim breaking ground on a new housing project in the capital. The images have not been independently verified.