A blaze tore through several rooms to the rear of St Raphael's church on Lowe Street on Friday afternoon, after charcoal was left in a plastic rubbish bin in the church's sacristy.

A secretary noticed large amounts of smoke coming from the building and immediately called triple-0.

Firefighters rushed to the scene and forced entry into the locked building, quickly working to contain the blaze.

Fire and Rescue NSW officers said the fire was at a critical stage, and was close to spreading to the main body of the church, where it would have become uncontrollable.

St Raphael's parish priest, Father Troy Bobbin, said the fire would have caused major damage if it had reached the building's woodwork and roof cavity.

''I suppose if I'm a Catholic priest I'm supposed to say that God's with me, I'm not supposed to use the word luck,'' he laughed.

''It's just a pain in the butt, really. I was disappointed, but it's one of those things that's an accident.''

Father Bobbin said the fire would not interrupt the church's usual activities.

An assessor will look through the damaged rooms on Monday, and insurance is expected to cover any repair costs.

''Virtually it just has to be repainted and recarpeted, I'd say all the furnishings in it … will have to be replaced, but nothing major,'' Father Bobbin said.

''[Charcoal] is a high-risk thing, we just need to be very careful, it just teaches me I need to put a better plan in operation.''

Father Bobbin said the smoke had also damaged linen and robes.

St Raphael's church was built in the 1950s.