A bushfire which tore through the West Australian town of Yarloop last week, killing two people and destroying at least 180 homes and other buildings, has broken containment lines.

Authorities said the breach happened near the intersection of Forrest Highway and Forrestry Road near Lake Preston.

A watch and act alert has been issued, with authorities saying homes in the area may be under threat.

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It does not include Preston Beach, but does include farming properties in the area.

Fire authorities have also issued a watch and act for the South West towns of Cookernup and Waroona saying the fire is also threatening containment lines there.

The fire was sparked by lightning and has been burning across parts of WA’s South West since January 6.

The blaze has burned through more than 70,000 hectares of land and its perimeter has grown to 327 kilometres.