Fire investigators examine the burnt-out restaurant. Picture: Bianca De Marchi Source: AdelaideNow

The blast blew out the front windows of the Pars Pizza store in Kilkenny and left the interior blackened and twisted.

One man, believed to be the pizza shop's manager, was taken to Royal Adelaide Hospital. Doctors there would not reveal his condition

Employees from an adjacent service station said they saw the shop on fire after the explosion.

One, Fouad Fandi, said the injured man was found in the middle of the road.

He said those witnesses thought the force of the explosion had thrown him on to the road.

"He (the pizza shop manager) is from Iran and he's only been in Australia for eight months and at the pizza shop for three months," he said.

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"He's a really nice man. He comes in a lot and always talks to me."

Mr Fandi said he believed a woman who often worked in the pizza shop had not been in the store when the explosion happened.

Investigators are working to determine what caused the explosion.