Sydney's Catholic leader believes Christians around the world are "under siege" and hopes the fire at Paris' Notre-Dame Cathedral was not a deliberate attack.

Investigators believe the blaze, which destroyed most of the roof of the 850-year-old architectural icon, was an accident possibly linked to renovation works.

Archbishop Anthony Fisher. Credit:AAP

But Archbishop Anthony Fisher said after hearing of a recent "catalogue of fires" at churches in France, "it really struck me that we are, in some ways, under siege".

"Particularly at this time, we know there are those in the world who are opposed to all religion or opposed to our religion and it looks like some of them are determined to make that clear by burning down our buildings," he told 2GB radio on Thursday.