Volunteer firefighters were met with eerie scenes as they responded to a raging bushfire in Bunyip National Park in eastern Victoria.

An estimated 6,300 hectares of land have burnt so far with 25 fires blazing across the south Australian state since Friday.

Local fire authorities have expressed concerns that strong winds and hot temperatures will fuel the blaze.

Up to 850 people were battling the Bunyip fire on Sunday, assisted by 120 fire engines and 20 aircrafts.