All northbound lanes of the Hume Freeway have been closed at Donnybrook Road after the collision.
It comes as tens of thousands of people in the state remain without power and some trains have been suspended after severe storms hit the state.
Images showed the truck had jack-knifed and a power pole hung precariously to the side of the freeway.
Traffic was slowed significantly in the area, with a seven-kilometre trail of vehicles near the Amaroo Road exit causing significant delays.
A spokesperson from the Victorian Department of Transport said motorists heading away from Melbourne would be sent onto Donnybrook Road to then use Merriang Road and the Wallan-Whittlesea Road back to the freeway.
Melbourne-bound delays had started at Beveridge driving towards the incident.
It’s unknown when the freeway will reopen.
Meanwhile, major power firms confirmed more than 30,000 people have lost power, while Public Transport Victoria said some regional and metro train lines have been affected.
Buses are replacing trains on the Craigieburn line between Broadmeadows and Craigieburn, on the Hurstbridge line between Greensborough and Hurstbridge, and on the Seymour/Shepparton line between Southern Cross, Wallan and Seymour.
“Some train services continue to run on either side of the affected stretches,” a spokesperson said.
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“We ask passengers to check station platform displays, listen for announcements, and allow extra time.”
Port Melbourne as well as Keilor Downs, Taylors Lakes, Tarneit and Melton in the city’s west are affected by power outages.
In regional Victoria homes and businesses in Warrnambool, Geelong, Ballarat, Bendigo, Rochester and Kyabram have also been cut off.
The unplanned outages are under investigation, with crews working to restore power, Powercor said.
Forecasters have warned of possible flash flooding, with the Bureau of Meteorology issuing a severe weather warning and forecasting more storms to come.
The BOM said the thunderstorms are moving east and south-east.
Drivers are also being told to avoid the roads, amid fears of dangerous conditions including possible fallen trees.
“If driving conditions are dangerous, safely pull over away from trees, drains, low-lying areas and floodwater,” the alert said.
“Avoid dangerous hazards such as floodwater, mud, debris, damaged roads and fallen trees.”
A separate severe thunderstorm warning has been issued for parts of the Central, Mallee, Northern Country, North Central and Wimmera districts.