A street performer has plunged to the ground from a towering unicycle as bystanders froze in shock.

Footage believed to be filmed in Adelaide's Rundle Mall shows the man confidently riding the one-wheeler and holding a flamethrower as a large crowd watches him.

But the daredevil loses his balance, falling to the ground, before laying still for a couple of seconds.

Onlookers screamed at the unexpected incident and were left paralysed, unsure if the man was still conscious or if it was all part of the act.

One man eventually runs towards the man to see if he is okay and snatches the torch from his hand.

A number of other men also rush to help lift him off the ground.

A young boy from the audience is heard saying: 'Are you okay?'

The daredevil loses his balance, falling metres to the ground, laying still for a couple of seconds

Some users who commented on the footage suspected the fall was part of the act.

'I thought it was part of the act,' one wrote.

'Now we are going to demonstrate the bystander effect. 3. 2.1. Dudes knocked out and hand getting toasted. Like 200 people standing by,' another wrote.

Many praised the young boy's kindness for asking the performer if he was okay.