The WA Government has confirmed the state budget is forecast to record its first surplus in six years, with the extra funding to be committed to the Metronet public transport masterplan.

Key points: The WA Government announces first surplus in six years of $1.02 billion

The WA Government announces first surplus in six years of $1.02 billion State debt has been revised down by $2 billion to $37 billion

State debt has been revised down by $2 billion to $37 billion The Opposition says the windfall is thanks to additional GST and royalty revenue

The Government had previously forecast a return to surplus in 2020-21 of $1.3 billion.

But in today's mid-year review of the state's finances, Treasurer Ben Wyatt revealed a surplus of $1.02 billion now predicted one year earlier in 2019-20.

The mid-year review revealed an extra $700 million has now been allocated to Metronet projects since the May budget.

Treasurer Ben Wyatt is forecasting a $1.02 billion surplus in 2019-20. ( ABC News: Eliza Laschon )

"We've provided an extra $300 million for Metronet for what we call projects under development, which also includes the Morley-Ellenbrook line," Mr Wyatt said.

"That has been partly funded, we have allocated the $185 million from the sale of PEXA to that amount.

"Because what we're now seeing … is once it's gone through the Infrastructure Australia process we have a good understanding of the cost and the route etcetera.

"This is now just really starting to budget for [the projects] on a provisional basis."

Boost for struggling home buyers

Under the Metronet plan, new train lines will run to Ellenbrook and Perth Airport; a line will link Thornlie and Cockburn; and extensions will also be built to Yanchep and Byford by 2023.

WA Labor's Metronet plan. ( Supplied: WA Labor )

As previously announced, a total of $420 million has also been allocated for a boost to the state's low deposit loan scheme Keystart, and an extra $150 million has been allocated for survivors of institutional child sex abuse.

This financial year the state will record a smaller deficit than originally forecast, at $674 million.

State debt has also been revised down by almost $2 billion to $37 billion in 2018-19.

Despite the revision, WA will pay almost $1 billion dollars in interest annually on that debt.

"The economy in WA continues to improve and it continues to improve well," Mr Wyatt said.

"To be honest, [the state's finances] are better than I expected … halfway [into my term] … economic growth is delivering faster than I expected."

But Mr Wyatt admitted a struggling housing market and volatile commodity markets remained a cause for concern.

The Government expects its major Metronet plans will be complete by 2023. ( Peter Major: User submitted )

No credit from Opposition

WA Liberal leader Mike Nahan refused to give the Government credit for delivering a surplus sooner than expected.

"I wish I was … as lucky as that, $2.4 billion dollars in GST and $1.3 billion dollars in additional royalty revenue," Dr Nahan said.

"That would have gone well four years ago."

Mike Nahan was not prepared to give the State Government any credit for delivering an early surplus. ( ABC News: Eliza Laschon )

Dr Nahan called on the McGowan Government to lessen the burden on households, saying families had struggled to cope with an average increase in fees and charges of $700 over two years.

The Treasurer indicated increases to household fees and charges in next year's budget, particularly electricity, would be kept as low as possible.

But he would not put a figure on the increase and Treasury warned it could have a significant impact on the state's finances.