Critics say it is inherently dangerous and, for the most part, illegal.

But longboard skateboarders say their rapidly-growing sport is largely misunderstood.

They are urging authorities to work with them rather than against them to find ways for them to train both safely and legally.

Until 18 months ago, only a handful of people were longboarding in South Australia.

But now there are hundreds, many of them under 18.

The longboards are bigger, tougher versions of skateboards and designed to tackle the twists and turns of steep descents.

Some of the best ones locally are in the Adelaide Hills, explains teenager Jayden Mitchell.

"You'll start out on legal roads but as soon as people sort of just really start to get into it they'll just want to find bigger and better hills and most of them are situated on illegal roads to skate on, but that's just what we've sort of been pushed to," he said.

The law allows skateboards to be used on certain roads but not many.

Roads with a dividing line or median strip cannot be used and riding is not allowed at night.

Skate shop owner Sean Flynn says longboarders do not set out to be lawbreakers.

A few South Australians now compete on the world longboarding circuit.

That is where 16-year-old Jayden Mitchell is hoping to end up.

"Eventually, definitely. [I] will be starting to go to interstate events later this year hopefully and then just keep at that and work my way up but it might take a while," he said.

The teenager needs to practice and that means riding illegally, followed by a support car.

He has also worked to improve the sport's image, recently holding a legal competition which raised hundreds of dollars for the Adelaide Women's and Children's Hospital Foundation.

The state's only major event, the Collingrove Cup, was held for the first time last October in the Barossa Valley.

This year's event again is attracting entries from all over the country, a competition organisers hope will help legitimise longboarding in South Australia.

In some parts of the United States authorities are trying to ban the sport, but longboarders here are hoping to find a happy medium.

Burnside councillor Anne Monceaux says she often comes across longboarders on the roads around Mount Osmond and is worried someone might be hurt.

"I sympathise with them in terms of there not being a place but then it would be wonderful if we lived in a wonderful world where a space could be provided for them, or roads could be closed," she said.

Police Superintendent Linda Fellows says roads need to be kept safe for all users.

"The fact is that the law doesn't allow for the road to be used as a racetrack and it's not a place for recreation and the law applies equally to a lot of other devices like that so maybe rollerblades or rollerskates, or scooters or unicycles even," she said.

About a decade ago, downhill mountain bikers were facing similar issues to those the longboarders now face.

National parks were the best places to practise, but bikes usually were banned there.

They lobbied for a dedicated site and in 2006 the Eagle Mountain Bike Park opened.

But longboarders are yet to form any sort of lobbying organisation, despite being keen to talk to councils and other authorities.

Any move for change would require councils to make risk assessments and consider disruption caused to local residents and the issue of public liability insurance.

Longboarders say their sport is not as dangerous as it looks and the self-regulating community is vigilant about safety.

"If anyone skates beyond their ability, they're pulled up pretty quick. If anyone skates without a helmet they're told off quite quickly as well," Sean Flynn said.