At the parade, Kim insisted there had not been a single Covid-19 case in the country, thanking citizens for staying healthy
Thousands of North Koreans have packed into Pyongyang's Kim Il Sung square to pledge their support for the government -- all of them wearing masks, unlike at a military parade only two days earlier.
Authorities held the rally on Monday at the start of an "80-Day Campaign", a mass mobilization drive to boost the economy ahead of a ruling party congress in January.
Such efforts, often dubbed "battles", feature extra-long work hours and additional duties and are commonplace in North Korea in the lead-up to major events.
Troops, workers and students, all of them wearing facemasks, packed into the square, holding slogans including "Let's keep pace with the steps of our dear leader, Comrade Kim Jong Un."
It was a change from the military parade the North held at the weekend as part of the commemorations for the ruling party's 75th anniversary, when neither Kim nor any other participants had their faces covered.
Pyongyang closed its borders in January to try to prevent infection by the coronavirus that first emerged in neighbouring China, and at the parade -- when the North showed off its latest missiles -- Kim insisted there had not been a single case in the country, thanking citizens for staying healthy.
Kim -- along with other officials -- was also pictured unmasked watching a "Mass Games" propaganda display on Sunday, while spectators were seen wearing face coverings.
The ruling party anniversary comes during a difficult year for North Korea with the coronavirus pandemic and recent storms adding pressure to the country, which is subject to international sanctions over its banned nuclear weapons and ballistic missile program.
State Affairs Commission vice chairman Pak Pong Ju told the rally the next 80 days were "a very important and significant time period for our revolutionary advance", the official Rodong Sinmun newspaper reported.
"If we miss out on this lifetime opportunity and delay our advance at all, we could end up facing terrible and multiple challenges on our way forward."