Housing developments across Sydney's west and south-west will be given a $262 million boost ahead of Tuesday's budget, the New South Wales Government has announced.

New South Wales Treasurer Gladys Berejiklian said the money, from the Government's housing acceleration fund, will be used to pay for a number of infrastructure projects, in particular the building of new roads.

"We appreciate that you can't just build dwellings without having the associated roads and utilities in place," she said.

"We're providing the funding so that those dwellings can go up as soon as possible."

A total of $140 million will go towards the construction of Hills Road in Lidcombe, $22 million to fund widening and an upgrade of Hamblen Road in Blacktown, and $40 million for road upgrades in Camden.

Ms Berejiklian said the funding would support 58,000 new homes.

"We need to ensure we have enough housing to cater for the growing population - that's why it is so important that we keep unlocking new land by providing funding for the necessary infrastructure," she said.

"Building new communities and increasing supply is the best way to put downward pressure on housing prices.

"We have already seen record approvals under this Government, and we will continue to work hard to increase supply."

Another $62 million will go to the Greater Sydney Commission over four years to help deliver more homes, jobs and infrastructure across the region.

Money for WestConnex, not new funding: Opposition

But the NSW Opposition Deputy Leader Michael Daley said the money was being used to build an M4 motorway off-ramp, which he said fell within Stage One of the WestConnex project.

"More than half of that $260-million announcement today is going, not to supporting the building of new homes, but to pay for bits and pieces of WestConnex," he said.

"The Government is not doing what they said they would do."

Mr Daley said the announcement was "jiggery-pokery" from Ms Berejiklian, and the money promised was not additional funding.

"Here we have today, the Treasurer Gladys Berejiklian making a re-announcement from November, and it's a re-announcement of the worst kind," he said.

In November last year, Planning Minister Rob Stokes and Roads Minister Duncan Gay announced $140 million to go towards a M4 westbound off-ramp at Lidcombe.

Ms Berejiklian's second budget will be handed down on June 21, with some details already filtering out.

Housing affordability remains a lingering concern for NSW residents, particularly those in Sydney, and new rules for foreign ownership are being introduced.

Some of the other key budget announcements include a $3.8 billion plan to bring 3,000 new prison beds into the NSW prison system over the next four years and a $300 million budget package for victims of domestic violence.