California has joined five other American states to legalise recreational marijuana use.

The new laws – which kicked in this morning – mean you no longer require a medical license to purchase and use the drug.

The sale of marijuana is still subject to strict conditions however – it must be purchased from a licensed dispensary, and you must prove you’re of legal age (21) to buy.

Overnight some excited about the new, relaxed laws camped out in order to be among the first to purchase pot, legally.

Steve De’Angelo, CEO of California’s largest dispensary, said it’s an emotional day.

An ecstatic customer after making a purchase and wearing his free t-shirt at the Harborside cannabis dispensary in Oakland, California. (AAP)

“I don’t know whether to be overjoyed that prohibition is over or be really enraged that it ever had to happen in the first place," he said.

"Just take a look at the data that's coming out of cannabis reformed states where we consistently see that the amount of alcohol consumption drops and the amount of pharmaceutical consumption drops.

"There's a whole range of associated public health benefits that flow from that drop in consumption in those substances.

"Binge drinking drops and teen-related suicide drops. In the first 20 states that reformed their medical cannabis laws, we saw a 24.8 percent reduction in fatal overdoses.

"My message to Australia is just watch what happens here. It's very predictable because we've seen it in other states."

A customer's cannabis items purchase at the Harborside cannabis dispensary in Oakland, California. (AAP)

Mr De'Angelo went to federal court to help argue the case for legalisation.

His dispensary, Harbourside opened at 6am to a line of people who braved cold conditions overnight to mark the historic occasion.

First in line was Jeff Deakin, with his wife and dog in tow.

“I’m probably going to go home and roll a joint and relax," he said, after buying an ounce.

California is one of six states to defy the federal government and change its state laws to allow legal pot use.

And residents say Australia should be watching.

“Just study what happens in California,” Mr De’Angelo said.

“See the jobs that are created, the way we disempower criminal cartels and the way that we raise hundreds of millions of dollars of tax revenue.”

Recreational cannabis is also legal in various forms in Germany and Uruguay.