Victorian authorities have issued an emergency warning for an out-of-control fire burning on French Island in Western Port Bay.

The blaze is travelling from the Ridge Track in an easterly direction towards Mt Wellington Road.

Authorities say the Mt Wellington road area could be impacted anytime between now and 8.30pm AEDT.

They have urged residents to leave now, before conditions become too dangerous, and warned that emergency services may not be able to help if residents decide to stay.

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Residents have been told to leave to Tankerton.

Aerial vision from helicopters show flames near buildings on the island.

French Island is the state's largest coastal island with a small population of just above 100 people.

It is also home to a substantial koala population which is largely free of disease, and occasionally used to repopulate areas on the mainland.

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More to come.