The company's Rocky Mount plant, one of the world's largest sterile injectable drug facilities, was struck by a tornado on July 19 and Pfizer had then warned that some drugs, including painkiller fentanyl, could see supply disruptions.

While Pfizer said on Monday that it expects production to restart fully at the facility by the end of the year, it warned that supply of medicines from the site would be affected until at least mid-2024.

Last month, the company had said it expects to restart production at the plant by the beginning of the fourth quarter.

Pfizer has restarted production of about 13 medicines, including those which are currently available through the company's emergency ordering process, and expects first shipments in the fourth quarter.

The company said it has added a new production line for sterile injectable drugs as part of the restart. The manufacturing line was approved earlier by the U.S. Food and Drug Administration.

The drugmaker's sterile injectable products include anesthesia, painkillers and anti-infective medicines for use in hospitals.

Pfizer estimates that medicines made at the Rocky Mount facility account for about 25% of its sterile injectables used in U.S. hospitals, or about 8% of the total U.S. hospital supply.

(Reporting by Bhanvi Satija in Bengaluru; Editing by Shounak Dasgupta)