More than 20,000 people crammed in for the biggest ever triple j One Night Stand concert, at St Helens on Tasmania's east coast on Saturday night.

Thousands of people lined up for hours before they were allowed into the free, all-ages concert headlined by Vance Joy and Peking Duk.

While many applauded the event, for some the overwhelming success had a downside, with hopeful partygoers waiting hours for food, a toilet, and some not even getting in.

triple j said this year's One Night Stand, the eighth such event for regional towns, was the biggest ever.

Joel Harwood, Bree Minnikin and Abbey Hollingsworth were among the record crowd. ( ABC News: Laura Beavis )

Bree Minikin from Launceston didn't regret lining up early.

"This stuff never happens in Tassie, it's such a good opportunity," she said.

Her friend, Joel Harwood wasn't surprised by the record turn out.

Peking Duk was one of the headline acts. ( Supplied: Damien Peck/triple j )

"Honestly, Tassie's come out, produced the goods, we're absolutely loving it," he said.

Scott Hall brought his son Josh with him.

"Why wouldn't you come? This is a once in a lifetime, it's just brought St Helens alive," he said.

The venue quickly reached capacity after gates opened at 3:30pm, and hundreds of people were left waiting outside the gates.

Earlier in the day, the town's main street was bustling with lines at cafes and service stations, with State Emergency Service volunteers called in to direct traffic and the steady stream of young people and families making their way to the recreation ground.

Accommodation in St Helens was booked out soon after the town was announced as the 2018 One Night Stand host.

On Saturday, tents had sprung up on vacant blocks and front yards throughout the town.

Elise Burney and Lara Howard were setting up their tent after driving up the coast from Hobart.

They were impressed by the lively atmosphere in St Helens.

Many said the event had brought St Helens "alive". ( ABC News: Laura Beavis )

"It's really cute for a small town to get so much notice and stuff, I've never seen it so busy before," Ms Burney said.

"It's always super quiet and it's just good to see the local businesses getting heaps of customers."

Nick Langoulant travelled from nearby Scamander with his sons Louie and Xavier to take part in a buskers festival organised to coincide with the One Night Stand.

"It's great, we came from Fremantle and there's a huge busking festival there but this is comparable, good crowds," the veteran musician said.

Vance Joy was also leading the bill. ( Supplied: Damien Peck.triple j )

Break O'Day Mayor Mick Tucker stood out from the crowd in an orange suit, echoing decorations festooned on streets and in businesses throughout the town.

He said the immediate economic impact of the concert was likely to be in the millions.

"This is going to put Tasmania on the map, St Helens on the map, and hopefully a lot of investment and jobs and opportunities will flow from it," he said.

Nick, Louie and Xavier Langoulant from Scamander performed in the busking festival. ( ABC News: Laura Beavis )

Cr Tucker said the level of goodwill and community cooperation created by the One Night Stand was just as important as the tourist dollars.

"The only thing we can ever hope for is to make our community a better place to live, make our children who leave home want to come back and stay here, have a job," he said.

"[The One Night Stand] is a one-off opportunity, once in a life time — you've got to grab it and run with it."

Madeline Hardwick was busy brewing coffee. ( ABC News: Laura Beavis )

Frustrated festivalgoers turned away

But not everyone was quite as happy.

Organisers were forced to turn away people after the venue reached capacity. Some social media users estimated the number turned away to be "in the thousands".

Disappointed punters said they had made long drives and waited in line for hours, before being turned away.

Steve Foogut wrote: "Not good enough, why wasn't it ticketed? We made a massive commitment of time and money to get there, then locked out, not fair, there were no warnings of missing out risk."

The crowd had grown to capacity by 4:30pm on Saturday. ( ABC News: Laura Beavis )

Heather Francis made a plea: "In the queue — apparently 20k inside but 2k+ still waiting for one out one in. Any chance????"

Many who made it inside were equally unimpressed with the long waits for food stalls and toilets.

Jade Allyse wrote: "Not a good set-up at all. Not enough food stalls or toilets, had to wait over an [hour] to get food. Ended up leaving. The event did not cater for the amount of people."

Paige Beddard posted: "I wouldn't bother, guys — it's an absolute shambles here."

Concertgoer Mia Hextall agreed the queues for entry to the event and for the toilets were long.

"Lining up for food and toilets was probably a bit ridiculous, but I enjoyed it," she said.

But volunteer Dina McGuinness said most of the crowd were patient and in good humour.

"The main question of the day was 'where's the toilet?' And it got to the stage where I just stood there and went 'toilet' and they said 'how did you know?'

"But they were so wonderful, they actually made our night."