The Red Cross announced that its experiencing a serious blood shortage and that the number of donors is the lowest its been in 20 years.

The nonprofit, which is the biggest supplier of blood in the United States, announced the emergency shortage Sunday and urged people to donate.

One of the most distressing situations for a doctor is to have a hospital full of patients and an empty refrigerator without any blood products, Dr. Pampee Young, its chief medical officer, said in a statement. A person needs lifesaving blood every two seconds in our country and its availability can be the difference between life and death, however, blood is only available thanks to the generosity of those who roll up a sleeve to donate.

The Red Cross saw a 7,000-unit shortfall in blood donations between Christmas and New Years Day. Even more troubling is the long-term trend: Over the last two decades, the number of people donating blood through the nonprofit has fallen by about 40%, it said.

As of Wednesday, Americas Blood Centers says that 22 of the 59 community blood centers in North America have a one-day supply or less of blood. Centers should have at least a 3-day supply to maintain normal operations, the group said.

A spokesperson for the Red Cross told HuffPost on Thursday that its seen an encouraging uptick in blood donations since announcing the emergency shortage. However, theres still a concern that poor weather will force blood drive cancelations in the coming days.

We urge those in areas not impacted by weather to give blood, Red Cross media relations lead Daniel Parra said. In order to overcome this shortage, the Red Cross must collect 8,000 additional donations each week this month.

The non-profit said a surge in respiratory illnesses like COVID-19 may impact turnout even further.

The long-term lack of donors may be explained by several factors, the nonprofit said. More people are working from home in light of COVID-19, making it harder for the Red Cross to provide people with convenient donation locations. And in recent years, changes to blood eligibility requirements and hospital protocols have also likely contributed to the shortage, the Red Cross said.

The shortage persists despite the U.S. Food and Drug Administration dropping all restrictions last year on gay and bisexual men donating blood a crackdown that started in the midst of the HIV/AIDS crisis in the 1980s.