A two-year-old boy has died and a girl suffered serious injuries after a tree fell on their house at The Patch in the Dandenong Ranges, east of Melbourne, as severe thunderstorms swept through Victoria last night.
Emergency services were called to the home about 9:00pm (local time) and had to rescue four adults and a five-year-old girl.
The girl was taken to Royal Children's Hospital with head, chest and leg injuries.
Two of the adults also received injuries, Ambulance Victoria said.
The tree fell on the house during a severe thunderstorm that swept across Victoria.
A woman was also taken to hospital with a broken leg after a tree fell on her in South Yarra in Melbourne's south-east.
More than 20,000 homes were without power across the state.
Power companies said electricity should be restored throughout the night and into the morning.
The Victorian State Emergency Service said it received about 700 call-outs in two hours.
Most of the calls were about fallen trees and traffic hazards, with nearly 500 requests for assistance coming from the Melbourne area.
The Metropolitan Fire Brigade responded to dozens of fallen power lines and road blockages.
A severe thunderstorm warning has been cancelled for Victoria.
A spokeswoman for Melbourne Airport said anyone with flights should check for delays with their airline.