A wildfire in the Alberta city of Fort McMurray could cost insurers as much as C$9 billion (U.S. $7 billion) making it by far the costliest ever Canadian natural disaster, according to research by Bank of Montreal Capital Markets.

BMO Capital Markets analyst Tom MacKinnon said that figure was a worst-case scenario based on a comparison to a wildfire in Slave Lake, Alberta in 2011. The bill for insurers was C$700 million in that fire, and the Fort McMurray fire is bigger and the properties more valuable.

“Since Fort McMurray is nearly 10 times the size of Slave Lake, a disaster of the same magnitude impacting nearly all of Fort McMurray could potentially lead to C$9 billion in insured industry losses,” MacKinnon said in a research note.

MacKinnon said a “more reasonable estimate” might be for total industry losses of between C$2.6 billion and C$4.7 billion, still by far the largest potential catastrophe loss in Canadian history.

The Slave Lake fire was previously Canada’s biggest insurance loss from wildfire. The costliest natural disasters were the C$1.9 billion in losses from the North American ice storm of 1998 and the Alberta floods of 2013.

The Fort McMurray fire, now in its fifth day on Thursday, has grown to five times its initial size and prompted the full evacuation of the area’s 88,000 residents.

The uncontrolled blaze has so far destroyed 1,600 buildings compared with 374 in the Slave Lake Fire, with another 19,000 potentially under threat.