WASHINGTON — All 50 states have now issued warnings about mysterious, unsolicited packages of seeds that people across the nation have received in the mail in recent weeks.

The packages appear to be coming from China, according to the U.S. Department of Agriculture. Photos shared by state agriculture departments show packages marked with labeling from China Post, which operates the official postal service of China. Some of the labels also indicate that the packages contain jewelry, although inside is typically a packet of seeds in clear, plastic packaging.

Wang Wenbin, a spokesperson for China’s foreign ministry, said at a briefing on July 28 that the address labels were forged and that China Post has asked USPS to send those packages to China for investigation.

USPS said in a statement that it was aware of the mailings and is in consultation with federal, state and local partners. The agency declined to elaborate further.

It’s not exactly clear who is behind the packages or what their intent is, but the leading theory is that they are part of a “brushing scam” — when third-party sellers send people items they didn’t order and write glowing product reviews on their behalf.

“At this time, we don’t have any evidence indicating this is something other than a ‘brushing scam’ where people receive unsolicited items from a seller who then posts false customer reviews to boost sales,” the USDA said in a statement.

The USDA said its Animal and Plant Health Inspection Service (APHIS) was investigating the situation along with the Department of Homeland Security’s Customs and Border Protection, other federal agencies and state agriculture departments.

The Canadian Food Inspection Agency is also investigating similar reports from residents.

Officials haven’t confirmed for sure whether these packages are an example of “brushing.” But it seems to be a likely possibility given that most of the recipients say they didn’t order the items, said Katherine Hutt, chief communications officer for the Better Business Bureau.

“When people get a package that they didn’t order, that’s one of the first things that we suspect,” Hutt told CNN.

If you happened to receive one of these packages, here is what the USDA and Better Business Bureau recommend you do:

• Contact your state plant regulatory official or APHIS state plant health director.

• Keep the packaging and mailing label intact. The USDA asks that people hold onto the packages until they receive further instructions from authorities.

• Don’t open the packet of seeds or plant them. Right now, their origins are unknown. The USDA is planning to test the contents of the packages to determine whether they pose any agricultural or environmental risks.

• Don’t discard them in the trash. They could end up in a landfill, where they could take root.