DENVER — Seeking a safe haven in Colorado’s legal marijuana marketplace, illegal drug traffickers are growing plants among the state’s sanctioned warehouses and farms, then covertly shipping the marijuana elsewhere and pocketing millions of dollars, according to law enforcement officials and court records.

In one case, the owner of a skydiving business crammed hundreds of pounds of Colorado marijuana into his planes and flew the cargo to Minnesota. In another, a Denver man was charged with sending more than 100 marijuana-filled Fed­Ex packages to Buffalo, where drug dealers divvied up the shipment. Twenty other traffickers were accused of relocating to Colorado to grow marijuana that they sent to Florida, where it can fetch more than double the price charged in a Colorado shop.

Among marijuana opponents, such cases confirm a longstanding fear that the state’s experiment in legal marijuana would cause more illegal trafficking in states where the drug is still forbidden.

Nebraska and Oklahoma sued in 2014, seeking to declare Colorado’s legalization unconstitutional, arguing that it sent a tide of illicit marijuana across their borders. The Obama administration has urged the Supreme Court to reject the suit.

No one knows exactly how much marijuana leaves Colorado. When shipments are seized, it’s often impossible to prove where they’re from. But ‘‘there’s no question there’s a lot more of this activity than there was two years ago,’’ said Colorado’s US attorney, John Walsh.

Some in the legal industry say police exaggerate the problem. Lawmakers last year limited unregulated growers to no more than 99 plants in an effort to crack down on those selling untaxed marijuana.

The US government allowed Colorado’s experiment on the condition that the state act to keep marijuana from migrating to places where it is still outlawed and out of the hands of criminals. Among other safeguards, Colorado requires growers to be licensed and use a ‘‘seed-to-sale’’ tracking system to monitor marijuana plants.

The Colorado Department of Revenue’s marijuana division cites shops if marijuana is unaccounted for but ‘‘after it’s sold, we have very little control,’’ director Lewis Koski said.