After Hurricane Maria pummeled Puerto Rico on September 20, the nation’s drug supply and hospitals should brace for their own beating in the next two to three weeks, head of the US Food and Drug Administration Scott Gottlieb warned in an interview with Reuters Tuesday.

With more than four dozen FDA-approved pharmaceutical plants, Puerto Rico manufactures 10 percent of drugs prescribed in the US. The list of drugs made there includes 13 of the world’s top-selling brand-name drugs, such as Humira, the rheumatoid arthritis drug, and Xarelto, a blood thinner for stroke prevention, The New York Times reported. Some of the medicines made there are made nowhere else.

“Some of these products are critical to Americans,” Scott Gottlieb told a congressional panel last week. “A loss of access could have significant public health consequences.”

Weeks after the hurricane hit, the territory is still limping from the devastation. Just 16 percent of electricity service has been restored, for instance. Drug makers are still producing some products, but they face uncertain power supply, difficulty getting materials, and a work force also struggling to recover.

“A lot of companies say they’re online, but they basically have one of five lines running at 20 percent or 80 percent or 50 percent,” Gottlieb told Reuters. “They are not manufacturing at full capacity. They are manufacturing well short of that.”

It’s unclear when manufacturing will be back to full capacity, he added. The agency has identified 40 medicines that are in danger of seeing shortages, including drugs for cancer, HIV, and arthritis. The agency has not identified the drugs by name.

The natural disaster has already knocked back the supply of small-volume saline and dextrose bags, which are widely used intravenous solutions. The Washington Post reported Monday that hospitals across the country are scrambling to find alternatives or make their own supplies of the common solutions. The bags’ manufacturer, Baxter International, told the Post that it was experiencing “limited production” at its Puerto Rican facility. The company was said to be “working to leverage our global manufacturing footprint to support alternative production of these products as we work to restore operations.”

Still, many hospitals reported that the shortage caused disruptions, frantic switches—and fear. “There remains great concern that treatment for children with cancer may soon be affected,” Peter Adamson, a pediatric oncologist at Children's Hospital of Philadelphia, told the Post.

Gottlieb told Reuters that shortages might come in the next two or three weeks.

Pharmaceutical companies that have facilities on the island include Merck & Co, Johnson and Johnson, Amgen Inc, Bristol-Myers Squibb Co, Eli Lilly and Co, Pfizer Inc, AstraZeneca, and GSK.