Seven miners were initially trapped after the collapse at the Unryul mine, a leading iron ore producer, on January 9, North Korea's main newspaper Rodong Sinmun reported. It said one was rescued 10 days later but six others were found dead.
The newspaper said the accident was the worst disaster at the mine in South Hwanghae province since it was established.
North Korea's highly controlled state media rarely report news that might be considered negative, and an admission of fault by the government is unusual.
The newspaper, run by the ruling Workers' Party, said the January accident occurred when miners were launching "all-out" efforts to fulfill an order by leader Kim Jong Un to produce more ore to be supplied to factories under a five-year economic development project.
The sole survivor, identified as Kim Kyong Nam, said the victims could have made it out safety when they heard the sound of the collapse, but didn't come out immediately because they first tried to check the situation in the mine, the newspaper said.