Officials across the United States are warning people who get unsolicited packages of seeds in their mailboxes to not plant them.
There are concerns that the seeds come from China and may contain invasive species.
"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," Ryan Quarles, Kentucky's agriculture commissioner, said in a video posted on the department's website.
Photos of packages that state agriculture departments posted on social media show seeds of different sizes, shapes and colours that arrived in white or yellow envelopes. State officials said some packages were labelled as jewellery and may have contained Chinese writing.
The Chinese Embassy in Washington, D.C., did not immediately respond the Reuters News Agency request for comment.
The United States Department of Agriculture said it is "aware that people across the country have received unsolicited packages of seed from China in recent days."
The agency is working with the Department of Homeland Security and states to protect U.S. agriculture and prevent the unlawful entry of prohibited seeds, according to a statement.
State officials have asked recipients to secure the seeds in sealed plastic bags until they are picked up by authorities.
