The Food and Drug Administration said on Monday that it had warned seven companies to stop selling products that claim to cure or prevent the coronavirus, saying such products were a threat to public health because they might prompt consumers to stop or delay appropriate medical treatment.

It was the first time that the agency, along with the Federal Trade Commission, had issued warning letters for unapproved products related to the coronavirus, which causes the illness Covid-19.

The companies that received the warnings were Vital Silver; Quinessence Aromatherapy; Xephyr (N-Ergetics); GuruNanda; Vivify Holistic Clinic; Herbal Amy; and The Jim Bakker Show, a joint statement said. The products cited in the letters were teas, essential oils, tinctures and colloidal silver.

The companies were asked to describe within 48 hours what they had done to correct the violations, or be subjected to legal action such as seizures or injunctions, the statement said. A task force had already worked with retailers and online marketplaces "to remove more than three dozen listings of fraudulent Covid-19 products," it added.

"There already is a high level of anxiety over the potential spread of coronavirus," Joe Simons, the chairman of the trade commission, said in the statement. "What we don't need in this situation are companies preying on consumers by promoting products with fraudulent prevention and treatment claims."

There are at least 545 cases of Covid-19 in the United States. California, New York, Oregon and Washington State have all declared emergencies over the spread of the virus, and at least 22 people have died from it in the United States. The F.D.A. and F.T.C. statement noted that there were no vaccines or drugs approved to treat the coronavirus.