Holy relics stored in the altar of the St Panteleimon Greek Orthodox Church appear to have escaped unscathed after fire tore through the Glenelg North building in Adelaide.

The Metropolitan Fire Service was able to stop the fire spreading, but the damage was so significant the church will be unable to host Orthodox Easter services over the coming weekend.

Parish president Nick Kapolos hailed the "miraculous" survival of the gold-plated box, which he said contains fragments of St Panteleimon's bones.

"In the altar where we keep them, everything else was pretty much burnt and the only thing that was left was the little box of the relics — not damaged, not even ashes on it, it was just sitting there," he said.

"Not a mark, no dust, no nothing — Father Michael just picked it up.

"As far as we see it, it is a miracle, because how can everything else burn but this is the only thing that survived?"

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Mr Kapolos said the relic was the most important artefact in the church, which lost an important Bible and cross to the fire which caused $100,000 worth of damage.

"We were basically saying 'Glory to God' … it was so good to see something saved," he said.

"The Christian faith is built on hope, and I've shed my tears earlier, but I'm now resilient and that's what our faith does."

It is not clear what caused the fire, and hundreds of worshippers will have to find somewhere else to mark Orthodox Easter.

"I've had phone calls non-stop all day, I've had former [state government] minister Tom Koutsantonis give a call as well, and even people that don't go to church have sent text messages," Mr Kapolos said.

A Catholic church in Glenelg has offered to host services as the Orthodox faith prepares for one of the biggest occasions in its calendar.