Bushfires in southeast Victoria over the past week have destroyed at least 31 houses and damaged another 70 structures.

Insurers are still assessing the extent of the damage in Bunyip, a small township east of Melbourne. The losses were serious enough to warrant the event being declared a catastrophe on Friday by the Insurance Council of Australia (ICA).

The declaration came after consultation with the Victorian Government and Emergency Management Victoria.

ICA says it could take several weeks to determine the full extent of the property losses. At least 100,000 hectares of land have been razed by the fires, which were sparked by lightning strikes over a week ago.

This summer has been a costly season for insurers, who are facing nearly $2 billion in losses from the Sydney hailstorm and “once-in-a-century” floods in Townsville.

The industry has recorded about $1.93 billion for claims arising from the two catastrophes, and the figure will rise as insurers continue to process claims and assess the damages.

Last December’s hailstorms have run up $1.04 billion in losses and the Townsville floods have cost insurers about $893 million.