America's first marijuana stores open

America's first retail stores selling marijuana have open for business in Colorado, putting the western state in the vanguard of the country's evolving attitudes on legalising the drug.

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Officials in the state famous for its ski resorts and breathtaking mountain vistas have issued 348 retail marijuana licences - including for small shops - that allow for the selling of up to 28 grams of pot to people aged 21 or older starting January 1.

Washington state on the US Pacific coast will follow Colorado several months from now, when it also allows stores to begin selling cannabis.

Both states legalised recreational consumption of marijuana in referendums held in November last year, but the new rules coming into force allow cannabis shops.

State officials here anticipate that marijuana sales will generate some $US67 million ($A75 million) in annual tax revenue.

Colorado's branch of the National Organization for the Reform of Marijuana Laws (NORML) said everyone will benefit.

"It will mean jobs, tax revenue for the state and local jurisdictions, increased tourism and a developing progressive new industry in Colorado," NORML lawyer Rachel Gillette said.

"It will also have an impact in that marijuana sales will be brought out of the shadows and the black market," she added.

Michael Elliott, head of the Medical Marijuana Industry Group, noted that Colorado has licensed medical marijuana businesses since 2010, but said the influx of tourists for recreational use of pot could lead to shortages.

"It's tough to know whether supply will meet demand, mainly because it's tough to know the impact of tourism on this new market," he said.

"It looks like demand will exceed supply, so I anticipate that prices in Colorado will go up ... But as time goes on, more businesses will open meaning there will be more supply," he added.

Tax collectors are eyeing the revenue the newly legalised trade will generate, while cannabis growers and others are also rubbing their hands in anticipation.