DENVER (AFP) - It was barely dawn when people began lining up outside the Denver Kush Club on Wednesday, turning up their collars against the sleet and wind.

But a little winter weather wasn't about to put them off - they were making history.

"I'm in no hurry. I've waited my whole life for this," said 43-year-old Mr Scott Van Pelt, who drove seven hours from notoriously conservative Texas to be among the first to legally buy marijuana for recreational use.

Colorado and Washington approved the recreational sale of cannabis in November 2012 referendums, and pot shops were allowed to open on Jan 1 in Colorado and later in the year in Washington.

Medical marijuana is already legal and regulated in 19 American states, and has been allowed in some cases for the past 20 years. And in most of them, private consumption of cannabis is not classified as a crime.

The start of retail sales marked not only a legal turning point in how marijuana can be purchased, but also in terms of how it will be consumed and the market it will create, if the customers at the Kush Club are any indication.

A sour, earthy smell permeated the shop's two rooms.

Ms Amber McFadyen, 38, stood at the front room counter for about 10 minutes browsing products, rocking back and forth on her feet and pressing her finger to her lips as she tried to decide.

She was less interested in the jars filled with weed of varying strengths, labelled Strawberry Kush, Amnesia, Sour Diesel, Golden Goat and Green Crack.

Instead, she was more drawn to the edibles, which included bars of cannabis-laced chocolate like Cookies and Cream, Peach Dream, Blueberry Bliss and the Monkey Bar.

"Do you have any gummy bears?" she asked the girl behind the counter.

No luck, but there were plenty of other sweets, from blueberry belt strip candy to "gemstones" in juicy pear, raspberry, fruit loops and other flavors - all laced with tetrahydrocannabinol (THC), the active chemical in cannabis.

Her husband, Scotland-born Mr Kieron McFadyen, 42, already had his mind made up.

"I think I'm just going to get a quarter of whatever the happiest is," he said.

In the end, they walked out with US$260 (S$328) worth of goods stuffed into a little white paper bag stapled at the top. And, they said, they are not even regular marijuana users.

"We live two blocks away and we got up this morning and said, 'Why not?'," said Ms Amber.

Kush Club co-owner Darin Smith said he expects up to 400 customers per day, now that the law has changed, compared to about 100 when the shop only sold pot for medical use.

He opened the Kush Club - named after a type of marijuana - four years ago.

"I think now we're just bringing it out of the shadows, giving people the choice whether they want to smoke or not," said Mr Smith, 29.

The potential market for marijuana sales is huge.

It is expected to grow by 64 per cent to US$2.34 billion in 2014 with recreational pot added in Colorado and Washington, according to ArcView Market Research, which tracks and publishes data on the cannabis industry.

"It just makes it an item of commerce, like going into a liquor store," said a grey-haired Mr Charles Pierce, 61, who was buying marijuana to use for the first time in two years.

Critics of recreational sales of marijuana in Colorado say it will create a culture of "pot tourism" in the state.

"I don't think this is something that Denver wants to be known for as the pot capital," said Ms Amber McFadyen.

But for the Kush Club's Smith, it's part of business. "It will absolutely go hand-in-hand with tourism," he said.

Tourism is the second largest industry in Colorado. More than 60 million people visited the state in 2012, according to the consulting firm Longwoods International, which conducted research for the Colorado Tourism Office.