The agency has also been monitoring the nation’s drug supply chain, identifying several drugs that could face shortages if the epidemic in China and elsewhere lasts for months. It has said that at least one drug is currently in short supply in the United States because of difficulties related to the coronavirus, but has not said which one. Hospitals have struggled for years with hundreds of shortages of essential medicines, many of them generic products made overseas.

“At a time when there are shortages of medicines — critical medicines — there’s a lot of untoward activity that can take place, like counterfeits and poor quality products,” said Rosemary Gibson, an expert on China’s drug supply who is a senior adviser at the Hastings Center, a nonpartisan bioethics research institute. “The bottom line is, who is going to be checking?”

Ms. Gibson said that while the agency does spot checks of imports, “the public needs assurance and transparency on what exact steps are being taken for every shipment of a prescription drug coming from China.”

Dinesh Thakur, a drug-safety advocate who exposed widespread quality problems as a former executive at the Indian drug maker Ranbaxy Laboratories, said Indian drug makers have been reporting that they still have about a six-month supply of active ingredients made in China. If they begin to run out, “Guess what’s going to happen?” he said. “You are going to have problems. They will happen in India. The question is, how do we enforce that?”

When the F.D.A. does cite pharmaceutical plants for problems, they frequently happen in India and China, according to a report by Barbara Unger, a consultant who tracks F.D.A. regulatory actions around the world. During the 2019 fiscal year, she found that the agency issued 16 warning letters to plants in India and 15 to facilities in China, accounting for a majority of the 43 warning letters issued that year to overseas drug manufacturing plants. It was not clear whether those warnings were issued after routine inspections — the type being halted because of the coronavirus outbreak — or after inspections for cause.