Medical cannabis-based products are available in about half of US states. JACK GUEZ/AFP/Getty Images

States that have legalised the use and sale of marijuana in the United States will create 400,000 new jobs by 2021 and generate $40 billion (£29.5 billion) according to a new study into the legal cannabis sector.

If proven accurate, the estimate from consultancy firm Arcview (via AFP) would mean a rise of 150% in the sector from the $16 billion in revenue recorded in 2017.

Arcview's study believes that direct purchases from consumers will amount to $20.8 billion, with the rest of the money generated indirectly by growers and other businesses not associated with the sector.

It also expects $4 billion to be created in taxes within three years and 100,000 cannabis industry jobs to be created in California alone by 2021, rising to 146,000 when indirect effects are accounted for.

The report states that just 100 of the 3,000 oulets and services in California have the required permits to trade in the product.

"Those that generally reported doing multiples of their typical day's business with a far more diverse and less experienced customer base that need a lot of hand-holding and educating from their bud-tenders," said Arcrview's Tom Adams.

"We were very cautious in projecting revenue growth from $3-billion to $3.7-billion in this first year of adult-use legality in California, but we'll have to revise that upwards if, as now appears likely, San Francisco and Los Angeles are going to get permits issued more quickly than we expected."

Jesse Arreguin, mayor of Berkeley, California, hailed the state becoming the largest legal market for cannabis in the world on Monday.

At an event he said: "I'm stoked about this historic moment, not just for Berkeley, but for the state of California."

Marijuana is legal for medical and recreational use in California, Nevada, Oregon, Alaska, Colorado, Massachusetts and Maine.

It has been legalised for just medical use in a further 23 states: Montana, North Dakota, Arizona, New Mexico, Minnesota, Illinois, Arkansas, Louisiana, Florida, Michigan, West Virginia, Ohio, Pennsylvania, Maryland, Virginia, Delaware, New Jersey, New York, Connecticut, Rhode Island, New Hampshire, Vermont and Hawaii.

The remaining 20 states have no laws legalising the drug.