Colorado has become the first state in the US to legally allow the sale of recreational marijuana.
Thirteen former medical marijuana dispensaries have been cleared by state regulators to sell cannabis to consumers.
Colorado officials expect the commercial cannabis market to ultimately gross $578m (€420m) in annual revenues, including $67m in tax receipts for the state.
Under a state constitutional amendment approved by voters, possession, cultivation and private personal consumption of marijuana by adults for the sake of just getting high has already been legal in Colorado for more than a year.
But starting New Year's Day, cannabis will be legally produced, sold to the general public and taxed in a system modelled after a regime many states have in place for alcohol sales.
Due to the novelty factor, operators of the first group of retailers slated to open their doors were anticipating a surge in demand for store-bought weed.
Workers at a warehouse in the Denver suburb of Northglenn were rolling hundreds of marijuana cigarettes by hand yesterday in preparation for the sales.
"We expect to have 2,000 joints ready to go by the time we open," said Robin Hackett, the co-owner of Botana Care.
She expects between 800 and 1,000 customers to visit her store the today.
The shop has hired a private security firm to help with traffic and parking issues that might arise.