The declaration, which gives the state and emergency services additional powers, was put into place last Thursday.
Mr Andrews said the extension was needed to manage what was likely to be a significant increase in bushfire activity over the next 48 hours.
The state of disaster covers East Gippsland, the Alpine region and the state's north-east.
Authorities are urging people to leave the Alpine region and all areas east of Bairnsdale, in East Gippsland, as the fire danger once again ramps up.
Another expected round of dry lightning, combined with a forecast wind change, could potentially cause fast-moving fires across the state from Friday.
"This is a really significant challenge for us," Mr Andrews said.
"We don't underestimate it. We don't lightly extend the state of disaster. We have done it because we believe that it will save lives and that, after all, is the most important thing."
Emergency Services Minister Lisa Neville announced yesterday the death toll from the fires had risen to three after authorities confirmed the car crash that killed "well-loved" firefighter Mat Kavanagh on Friday was fire related.
Residents stranded in isolated communities have been cutting their way out of bushfire zones to get through closed roads, prompting serious safety warnings from authorities.
In a warning posted on the Vic Emergency website yesterday, authorities begged people to wait until firefighters and the Australian Defence Force could clear roads and mark them as safe before attempting to drive out.
But with nearly 5,000 kilometres of roads to clear, authorities have warned it will take some time before roads are made safe.
"Residents must stop this immediately. It is not safe to drive on these roads until they have been treated for hazardous trees and other damage."
A State Control Centre spokesman said the official advice was for residents who are leaving East Gippsland to monitor VicRoads updates, plan a route out of the area and leave when possible to do so safely. But he said no-one should be trying to access closed roads.