Victoria's fire authorities are warning of a tough week ahead as fire conditions worsen around the state.

A 3,000 hectare bushfire near Portland in the state's far south-west has jumped a river and moved into a part of the forest which is more difficult to access.

The CFA had hoped to have it under control before the the hotter weather returned to the area, but it is now expected to more than double its size before it is under control.

The blaze is travelling in a north-westerly direction through the Lower Glenelg National Park and a watch and act alert has been issued for Mumbannar, Drik Drik, Greenwald and Winnap.

A community meeting is being held at Dartmoor to update residents.

CFA spokesman Joe Buffone says conditions would not get any better heading into the next few days.

"The whole of the state is basically gearing itself up and preparing for Tuesday, which will see the north of the state again at severe fire conditions," he said.

"And then the next day of concern will be on Friday as well. So from a Victorian perspective, it's very much in preparedness and dealing with the fires we have and, in particular, the one in Portland."

Mildura, in the state's north, is expected to hit 40 degrees Celsius today and tomorrow, while Bendigo will reach 41C today and drop to 35C tomorrow.