The regime ordered foreign journalists to prepare for a 'big event' on Thursday and is thought to have put a nuclear device in a tunnel at its Punggye-ri Nuclear Test Site.
Tensions in the region are running high after President Trump sent a US Navy strike group steaming toward the western Pacific in a show of force and North Korea warned of a nuclear attack at any sign of America agression.
North Korea's most important national day is on Saturday April 15 when North Korea commemorates birth anniversary of its founding president Kim Il Sung.
There were no indications the 'big' event on Thursday was directly linked to tensions in the region over the isolated state's nuclear weapons program.
Around 200 foreign journalists are in Pyongyang as the country marks the 105th anniversary of 'Day of the Sun'.
Officials gave no details as to the nature of the event or where it would take place, and similar announcements in the past have been linked to relatively low-key set pieces.