Hundreds of fans were turned away from Elton John's Adelaide concert last night after purchasing invalid tickets via the re-sale site Viagogo.

Approximately 200 people were turned away from the gates at Botanic Park last night, after being informed that the tickets they purchased were fake.

One concertgoer, a mother by the name of Samantha Wells, had bought tickets for her autistic son James' 22nd birthday, spending hundreds of dollars to see the musician live in concert.

More than 16,000 people arrived to see Elton John live in concert. (9News)

Samantha Wells and her 22-year-old son James were told their tickets were invalid. (9News)

Sadly, she bought the tickets via Viagogo, and upon reaching the concert ticket office she was informed that the tickets were invalid.

"This is something James really looked forward to, and when they said they were fake it was really upsetting," Ms Wells told 9News.

Incredibly, two unsuspecting strangers stepped in and bought tickets for the pair on the spot.

"This man and this lady lent over and said we're going to pay for your ticket, and it was just beautiful," said Ms Wells.

Thankfully, unsuspecting strangers bought the pair new tickets for the show. (9News)

South Australia's consumer watchdog has now launched an investigation into the matter.

Commissioner for Consumer Affairs Dini Soulio said he is working hard to establish how the tickets were sold.

"I've been in touch with Viagogo most of the morning to work out... get to the bottom of what's going on," Mr Soulio told 9News.