People in several U.S. states, as well as Canada and the U.K., have reported receiving unsolicited packages in the mail containing seeds from China. In the U.S., many state agriculture departments have warned citizens not to open or plant the seeds, although some recipients reported having done so already.

According to the Michigan Department of Agriculture, the seeds are usually sent in white packages displaying Chinese lettering and the words “China Post,” but others reportedly have yellow packaging. Most recipients are also saying that they did not order anything and that the packaging was labeled as jewelry, toys or earbuds. The seeds have varied in shape, color and size. Some recipients have reported ordering seeds on Amazon and receiving these seed packets.

Citizens in more than half of U.S. states have reported receiving unsolicited seeds, including in Arizona, Minnesota, Oklahoma, Ohio, Washington, Utah, Louisiana, Virginia and Kentucky.

“At this point in time, we don’t have enough information to know if this is a hoax, a prank, an internet scam or an act of agricultural bioterrorism,” Kentucky agriculture commissioner Dr. Ryan Quarles said. “Unsolicited seeds could be invasive and introduce unknown diseases to local plants, harm livestock or threaten our environment. If you have received such a package, do not plant the seeds, and immediately contact the Kentucky Department of Agriculture.”

The U.S. Department of Agriculture said it is aware of the “suspicious, unsolicited packages” of seeds, and the Animal & Plant Health Inspection Service (APHIS) is working closely with the U.S. Department of Homeland Security’s Customs & Border Protection, other federal agencies and state departments of agriculture to investigate the situation.

USDA is urging anyone who receives an unsolicited package of seeds to immediately contact their state plant regulatory official or APHIS state plant health director.

“Please hold onto the seeds and packaging, including the mailing label, until someone from your state department of agriculture or APHIS contacts you with further instructions,” the agency said.

At this time, USDA said it doesn’t have any evidence to indicate that the incident is something other than a “brushing scam,” where people receive unsolicited items from a seller who then posts false customer reviews to boost sales.

“USDA is currently collecting seed packages from recipients and will test their contents and determine if they contain anything that could be of concern to U.S. agriculture or the environment,” the agency added.

China’s Ministry of Foreign Affairs reported that the mailing labels on the seed packages were forged and is asking that the packages be returned to China for investigation.