Most of the destruction from a tornado that tore through eastern North Carolina on Wednesday and struck a large Pfizer pharmaceutical plant affected its storage facility, rather than its medicine production areas, the company said on Friday.

The drugmaker's ability to salvage production equipment and other essential materials could mitigate what experts feared would be a major blow to an already strained system as the United States grapples with existing drug shortages.

“We do not expect there to be any immediate significant impacts on supply given the products are currently at hospitals and in the distribution system,” US Food and Drug Administration Commissioner Robert Califf said on Friday.

An EF3 tornado touched down on Wednesday near Rocky Mount, ripping the roof off a Pfizer factory responsible for producing nearly 25 per cent of the American pharmaceutical giant's sterile injectable medicines used in US hospitals, according to the drugmaker.

Pfizer said on Friday that a warehouse for raw materials, packaging supplies and finished medicines awaiting release had endured most of the damage to its 1.4 million square foot plant.

An initial inspection by the company found no major damage to its medicine manufacturing areas, and all 3,200 local employees are safe and accounted for.

Pfizer Chairman and CEO Dr. Albert Bourla said staff are rushing products to nearby sites for storage and identifying sources to rapidly replace raw materials lost in the storm.

The drug company says it is also exploring alternative manufacturing locations across its US network to fill gaps in production while the North Carolina site remains closed for repairs.

The FDA's initial analysis identified fewer than 10 drugs for which Pfizer's North Carolina plant is the sole source for the US market, Califf said.

The Rocky Mount plant produces anesthesia and many other drugs needed for surgeries but does not make or store Pfizer's COVID-19 vaccine or the Comirnaty and Paxlovid treatments. Medications produced at that facility alone account for nearly 8 per cent of all sterile injectables used in US hospitals, Pfizer said on its website.

The FDA said it will complete in the coming days a more extensive evaluation of the products that might be affected and the current domestic supply of those medications. “Many weeks' worth” of the destroyed drugs should be available in Pfizer's other warehouses, Califf said.