Australian gaming tycoon James Packer is one of the nation's richest people but has experienced a turbulent few years, which included his candidly admitting he was scaling back his work commitments due to mental health issues.

The 51-year-old, whose wealth was recently estimated at A$4.94 billion (S$4.7 billion) by the Australian Financial Review, last month revealed his latest surprise: He has sold almost half his stake in his Crown Resorts gaming empire to Mr Lawrence Ho's Hong Kong-based firm Melco Resorts and Entertainment.

Mr Ho is the son of gaming tycoon Stanley Ho, known as the "casino king" of Macau.

Mr Packer, who is the son of the late Australian media mogul Kerry Packer, pocketed some A$1.8 billion from the sale of a 19.9 per cent stake in Crown. It seemed to be a fortuitous deal between the duo, who are both sons of tycoons and previously spent more than a decade as partners in gaming ventures until 2016.

But the sale has raised questions about the future of one of Mr James Packer's most prized projects - the development of a massive A$2.2 billion waterfront hotel and apartment tower and casino at one of Sydney's most prime locations.

The 275m-high Crown Sydney project, at the Barangaroo site adjoining the Central Business District, will include 349 hotel rooms, plus luxury apartments, some of which have reportedly sold for A$40 million each. It is due to be completed by 2021.

In late 2013, the New South Wales state government controversially revealed that it had granted permission to Crown Resorts to open a gaming venue at the complex. It will be for high rollers only. At the time, Mr Packer, who is from Sydney but now spends much of his time outside Australia, said: "I am going to do everything I can to try and make Crown Sydney the best hotel in the world."

But the licence for the site's casino specifically states that Mr Stanley Ho or his associates should not be involved. This was because of concerns over his alleged links to organised crime triads - allegations made by the United States authorities. He has denied the allegations.

Crown has previously said it had no links to the older Mr Ho. It said in 2014 that regulators in Australia had found the younger Mr Ho to be a suitable associate of Crown and that his business interests were found to be independent of his father.

But the regulator, the NSW Independent Liquor & Gaming Authority, said the latest deal will now trigger a fresh review. "The NSW Independent Liquor & Gaming Authority will now review all relevant issues when considering the required approvals and new probity checks for Melco Resorts' shareholding acquisition in Crown Resorts."

Mr Lawrence Ho told The Sun Herald earlier this month that he was willing to travel to Australia to meet regulators but said his father had no role in his casino business.

"My association with him is the fact that I am his son," he said. "But apart from that, I run my businesses and my life pretty much separate from him."

Several MPs in NSW have raised concerns about the status of Crown Sydney following Melco's purchase of the stake in Crown.

Greens MP Cate Faehrmann said it was implausible to believe that Mr Stanley Ho was not an associate of his son. "Serious concerns were raised about (Stanley) Ho's links to organised crime," she told 7News. "Surely these have not gone away."

Most gaming analysts believe that Mr Lawrence Ho is likely to pass the probity checks.

However, an editorial in The Sydney Morning Herald said the deal between Mr Packer and the younger Mr Ho was "anything but simple" and insisted the regulator should carefully review Mr Ho's involvement in the new Sydney casino. It said scrutiny of casinos was necessary because the sector was at risk of infiltration by money launderers, loan sharks and organised crime.

"It is hard to believe that NSW would have handed Mr Packer and Crown the right to develop the casino had it known that he was planning to step back so quickly," it said.

"The threshold must be especially high if Mr (Lawrence) Ho seeks a seat on the Crown board... Regulators are doing exactly the right thing in putting the Crown deal through the wringer and not simply taking Mr Packer's word."

The Crown Sydney project has already been involved in multiple battles, including various changes of plans and a lawsuit to ensure its harbour views were not obstructed. Construction on the tower is well under way, but the battles seem set to continue.