The full shutdown of a large section of the Tullamarine Freeway began at 10pm on Thursday night and will add an estimated 40 minutes to journeys between the city and the airport, as an estimated 100,000 vehicles a day snake through the north-west suburbs via lengthy detours.

The full shutdown of a Melbourne freeway for roadworks for such a long period is unprecedented and VicRoads says high summer, when traffic volumes are lower, is the best time to do it.

"This is the first time in Melbourne's history that we have closed a significant section of a major freeway for several days," Trevor Boyd, VicRoads' Director M80 Ring Road Upgrade, said.

"With traffic volumes 20 per cent lower and the weather at its warmest, it's the best time to do this work."