Only one week into Colorado’s history-making recreational marijuana industry, one shop has already sold out of pot, others fear they may soon experience the same fate, and perhaps as many as 100,000 people have legally bought the product at Colorado stores.

Industry advocates estimate Colorado stores have already done more than $5 million in sales — including $1 million on New Year’s Day — although National Cannabis Industry Association executive director Aaron Smith acknowledges those are “back of the envelope” figures. The owner of one store said she expects to make as much in sales in the first 10 days of January as she did all of last year selling medical marijuana — a welcome burst of business that has come with long days and little rest.

“I had a dream once that I opened my store and didn’t have any competition,” said Robin Hackett, a co-owner of BotanaCare in Northglenn. “I had no idea it was a nightmare.”

Fears of marijuana shortages pervade the young industry. On Wednesday, a sign hanging in the door to The Clinic location near Colorado Boulevard and Interstate 25 in Denver read: “We are currently out of recreational cannabis. Please check back tomorrow. Sorry for the inconvenience.”

Many shops have imposed caps on maximum purchase amounts well below the caps required under state law. Numerous store owners say they have sold out of marijuana-infused edible products. Toni Fox, the owner of 3D Cannabis Center in Denver, said she closed her store on Monday and Tuesday this week in order to restock and give her staff a break. The store saw nearly 500 customers on Jan. 1 and close to that each day afterward.

Even for stores that reported robust inventory, like High Country Healing in Silverthorne, owners said marijuana could become scarce across the industry if more stores don’t get their licenses approved and open to absorb the flood of interest.

“None of us could really prepare for what was going to hit us,” High Country Healing owner Nick Brown said Tuesday. “I think we all thought we would see huge demand and lines. But I don’t think any of us expected what has happened over the last six days.”

Well more than 10,000 people bought marijuana at Colorado’s recreational pot shops on Jan. 1, according to industry estimates and tallies provided by the stores. And, while that initial surge was expected, the sustained interest was not. Brown and several other store owners said they saw only a slight drop-off in sales in the days after Jan. 1. Extrapolating from opening-day numbers, as many as 100,000 purchases have been made in the eight days in which it has been legal for people over 21 to buy marijuana in Colorado after showing nothing more than identification.

“It’s been staying very, very steady,” said Lauren Hoover, the manager of the Breckenridge Cannabis Club.

Hoover said 1,500 shoppers passed through the store on Jan. 1. A typical day for medical-marijuana sales last year was 20 to 40 customers, she said.

In Denver, where 18 stores were licensed to be open for recreational sales on Jan. 1, four more stores have received licenses in the past week, according to city officials. Still, industry advocates expect supply crunches to last for a while.

“It’s going to be an issue in at least these first few months,” Smith said.

That’s because Colorado recreational marijuana stores — all of which previously operated as medical marijuana dispensaries — are currently required to grow what they sell. Commercial growing didn’t actually become legal until Jan. 1, the same day retail sales did. All of the marijuana being sold now comes from a one-time-only transfer of plants and inventory from the stores’ medical marijuana supplies.

In the short term, stores will be able to restock with mini-harvests of the transferred plants. But it will take until March or April before shops will have a full harvest of plants grown solely for recreational sale.

“The retail marijuana market will take a few months to settle, and we will be closely monitoring activity,” Julie Postlethwait, a spokeswoman for Colorado’s Marijuana Enforcement Division, wrote in an e-mail.

So far, Postlethwait wrote, state regulators have not taken any enforcement actions against a store.

John Ingold: 303-954-1068, jingold@denverpost.com or twitter.com/john_ingold