It is best seen within an hour after sunset low in the western sky.

The family of the two children who died in a house fire in NSW's Hawkesbury region have released an emotional statement about their "unimaginable tragedy".

The siblings have been named as Myla Summer-Lea Hughes, 10, and three-year-old River William Higgins.

"Today, with shattered hearts, we share the devastating loss and unimaginable trauma our family has suffered following the tragedy at Bowen Mountain," parents Skye Hughes and David Higgins said in a statement.

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"Our family's world has been forever changed."

David and three other children managed to escape the blaze at the home in Bowen Mountain, about 77 kilometres north-west of Sydney, early on Monday.

"At the time of the fire, five of the children were at the Bowen Mountain home, while one child was safely with their mother, Skye, in Queensland, where the family had been preparing to reunite and begin a new chapter together in their new home."

"This heartbreaking reality makes this unimaginable loss even more devastating for all who loved them."

An online fundraiser has been set up with the parents' permission.

"These precious lives were deeply loved, and this unimaginable tragedy has left the family facing profound grief, trauma and overwhelming loss," the fundraising page says.

The parents also thanked emergency workers, doctors and nurses, family, friends and the local community for their support.

"As we mourn this heartbreaking tragedy and navigate an unimaginable loss, we respectfully ask the media and the public to honour our privacy and protect our children," they said.

"We ask for the dignity to grieve and support one another without further intrusion and will not be commenting further at this time. 

"Thank you for your understanding, compassion and respect."

An appeal is being held for funds to help cover the costs of funerals and memorials, emergency accommodation, necessities, trauma counselling and the loss of the family home. 

The fundraiser has already received more than 600 donations and raised more than $55,000. 

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The closure caused major delays, with traffic backing up towards Hillsborough.

The trio from India were known as “hardworking and grateful” and worked in NZ from 2023.

Firefighters are working to contain the oil and diesel runoff.

Commonwealth Bank has forecast the impact of potential changes to the capital gains tax (CGT) discount and negative gearing could fall flat for prospective home buyers, with only a "modest" decrease to house prices.

In a pre-federal budget analysis, economists from the big four bank, Luke Yeaman and Harry Ottley, said reforming the property tax benefits would only have a modest impact on lowering house prices and increasing productivity.

It estimates house prices could fall by 1.4 per cent with changes to the CGT discount and 2 per cent if coupled with an abolition of negative gearing.

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"The largest benefit will be higher long-term government revenue and a stronger budget," the economists wrote.

"Additional short-term volatility in the housing market is likely though, especially at a time when the interest rate cycle and slower population growth is also shifting prices and market sentiment."

Commonwealth Bank said changing the two policies may help affordability, as the median house price exceeds $1 million, but it will not solve the housing crisis.

"Boosting supply is still the key," the economists said.

The government has been dancing around what will be included in its tax reform, but has confirmed that one of the measures on the table is changes to the controversial CGT discount and negative gearing.

Critics have blamed the two property tax benefits for contributing to the housing crisis, with a Greens-led Senate inquiry finding the CGT discount is flawed and benefits investors over first-home buyers.

Two Labor senators endorsed the inquiry's report.

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However, some industry experts like the Finance Brokers Association of Australia warn that changing the policies could disincentivise investment in the housing sector and place upward pressure on rent.

If reformed, it would be the first time the CGT discount is rolled back since the Howard government raised it to 50 per cent in 1999 and the first time negative gearing is changed since it was temporarily limited by the Hawke/Keating government in 1987.

Treasurer Jim Chalmers has refused to confirm or deny whether the two policies will be changed and said the federal budget has not been finalised.

"Intergenerational fairness is a really important way that we address some of the substantial and understandable issues in our budget, in our tax system and in our economy more broadly," he said yesterday.

"What we are determined to see is a fairer economy that works for more people, including for younger people."

Chalmers told Nine's Today that there are other changes they are making to soothe housing pressures.

"If we did go down that path, I would encourage people to look right across the board at everything that we're doing in housing, not one or two policies in isolation," he said.

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