Total fire bans have been declared across the state for Friday and Saturday when temperatures are expected to be the hottest so far this summer.

The Country Fire Authority has warned that both days present extreme danger across Victoria, parts of which are severely dry following a relatively dry winter.

The weather bureau has predicted that the mercury will reach up to 40 degrees in Victoria with strong winds on both days.

Melbourne is expected to have a maximum of 39 degrees on Friday and 41 degrees on Saturday.

CFA state duty officer Tony O'Day said Victorians were faced with "serious fire conditions".