Stocks of companies involved in the marijuana industry, medical or otherwise, have hit fresh highs after Colorado launched the first legal US sale of recreational pot.

Investors today took the huge lines outside pot retailers in Colorado as a harbinger of potential growth in the still-new industry.

With one study predicting a $10 billion-a-year industry by 2018, hopes are that the legalisation of private cannabis use could eventually divert the fortunes reaped by illicit growers and traffickers to shareholders.

Most of the companies involved though remain small and untested, and trade on over-the-counter markets.

The biggest gain Thursday was at the well-established MediSwipe, Inc, which sells transaction-processing systems to the medical industry.

In October the company launched a co-operative in Colorado to work with licensed marijuana industry participants, most of them too small to afford quality financial processing systems on their own.

GreenGro Technologies, which sells growing systems and equipment popular with pot farmers, spiked 52.3 per cent to 6.7 cents.

GW Pharmaceuticals, which focuses on medicines derived from marijuana, rose 5.7 per cent to $3.30.

MedBox jumped 57.2 per cent to $28.70. The company makes high-security storage and dispensing machines for controlled medicines, equipment used by marijuana distributors.

Shares of California-based grower Medical Marijuana Inc were up 22 per cent to 18.9 cents, and medicine-focused Cannabis Science surged 44.4 per cent to 7.4 cents.

Acknowledging the difficulty of gauging a mostly illegal industry, analysts put the size of the US market, legal and illegal, in the low tens of billions of dollars a year.

The largest state market is California, selling nearly $1 billion worth of marijuana a year for medical use