A tornado that damaged a Pfizer manufacturing facility in North Carolina is sparking concerns about worsening drug shortages in U.S. hospitals and highlighting the vulnerability of the domestic supply chain.

Pfizer said its facility in Rocky Mount, N.C., makes nearly 25 percent of the company's sterile injectable medicines used in U.S. hospitals. It sustained serious damage Wednesday by an EF3 tornado, according to the National Weather Service.

Pfizer said it was still assessing the damage to determine the impact on production, but all staff were able to evacuate. 

"We already have teams on the ground assessing the damage and supporting our colleagues, and we are working urgently to determine the best way to get back online as quickly as possible, while ensuring the safety of our people," CEO Albert Bourla tweeted on Thursday. 

The site is one of the largest sterile injectable facilities in the world, with more than 1.4 million square feet of manufacturing space, according to the company. It makes products including anesthesia, painkillers, therapeutics, anti-infectives and surgical muscle relaxants. 

Hospitals across the country are already seeing shortages of sterile injectable drugs, said Tom Kraus, vice president of government relations at the American Society of Health-System Pharmacists, and the tornado is likely to make that worse. 

"There are already 300 drugs that were in shortage before today. And many of those were sterile injectable drugs and like the ones manufactured at this facility. So, we are already in a state of crisis with drug shortages and this, obviously, has the potential to contribute to that," Kraus said.

But until the company details the extent of the damage and which drugs were affected, the specifics of any potential shortages aren't clear.

If there is a worsening shortage, hospitals can try to identify acceptable substitute drugs or different forms of a particular medication. If the situation warrants, the Food and Drug Administration (FDA) can also make policy changes to expedite the importation of certain drugs, like it is doing with the chemotherapy drug cisplatin. 

Part of the issue, Kraus said, is that there are only two or three manufacturers that make sterile injectable drugs because there isn't a huge financial incentive for companies to enter that market.

"We do not have enough manufacturing capacity for these products, particularly sterile injectable drugs, and we don't have a diversified manufacturing capacity for them," he said. "The fact that so much of these drugs are coming from one facility is a problem in and of itself" because there's no redundancy when something goes wrong. 

The U.S. is in the midst of an unprecedented shortage of medicine, ranging from ADHD pills to pain medicine to injectable cancer therapies. The reasons vary and include manufacturing quality control issues as well as demand surges.  

In a statement, the FDA said it was monitoring the situation. 

"The FDA is aware of this incident and are grateful that the plant’s employees are unharmed. We are following the situation closely as it evolves and are working with the company to understand the extent of the damage and any potential impact to the nation’s drug supply," a spokesperson said.