Voters in California, Massachusetts and Nevada legalized the recreational use of marijuana Tuesday, according to media projections, while three other states approved rules allowing medical use of the drug.
A similar measure was leading in Maine in incomplete returns, while a referendum in Arizona looked unlikely to pass.
The votes greatly expand the reach of legal marijuana in the United States.
Pot is already allowed in the western states of Colorado, Washington, Oregon and Alaska and the capital, Washington.
The new laws create a vast swath, mostly in the Western US, where adults can legally grow, buy and consume marijuana and cannabis products.
Marijuana remains illegal under federal law, but more than 60 million Americans will now live in jurisdictions where it is legally available under state law.
The new laws are likely to accelerate an already snowballing marijuana legalization movement in the United States.
California's pot market alone is estimated at 1.6 billion dollars, and could potentially grow to 6.4 billion dollars by 2020, according to market researcher ArcView.
Before Tuesday's votes, half of the 50 states already allowed medical marijuana for qualified patients.
In votes Tuesday, Florida, Arkansas and North Dakota joined them in approving marijuana for medical purposes. A measure expanding medical marijuana access in Montana was leading as votes were counted, according to news reports.