Victoria has amassed a $9 billion war chest to help pay for a big-spending infrastructure, health and education agenda ahead of the 2018 state election.

Booming revenues from Melbourne's indefatigable property market, population growth, rising employment and a GST windfall have tipped billions of dollars of extra revenue into the Andrews government's coffers.

Labor's second budget, to be delivered on Wednesday, will predict a $2.9 billion surplus next financial year. That represents a massive $1.4 billion upgrade from Treasury's last estimate for 2016-17, made less than six months ago.

But the state's finances are expected to remain strong in the lead-up to the November 2018 election and beyond, with a $1.8 billion surplus expected for 2017-18, rising to $2.1 billion 2018-19 and $2.5 billion in 2019-20.