VICTORIAN Police Commissioner Christine Nixon says all fire-devastated areas will be treated as crime scenes to determine if arson's involved.

The death toll in the devastating bushfires has risen to 108 this morning and it's feared it could still go higher in what's now the nation's worst natural disaster.

Ms Nixon's told the Seven Network investigators are already at the Churchill fire in the Gippsland Valley.

She says there's good evidence from the speed at which it took off that it was deliberately lit.

Forensic investigators have also begun work in the Kinglake area where most of the deaths occurred.

There are still 31 fires burning across the state this morning which authorities warn some could take weeks to contain.

AAP