The announcement comes after the Crown Princess cancelled her planned attendance at a concert at Trondheim Cathedral tonight.
Mette-Marit now has daily symptoms, Norwegian media report.
"The Crown Princess needs more rest and her condition changes more quickly than before," a press release from the Royal Palace states.
"This means that changes to her official program can occur more frequently and with shorter notice than we are used to."
Pulmonary fibrosis is a chronic disease that causes scar tissue to form in the lungs. The scarring causes coughing, fatigue, shortness of breath, and recurring lung infections.
