Saudi Arabia has put a value of up to $1.71 trillion on energy giant Aramco in what could be the world's biggest IPO. 

But the valuation missed Crown Prince Mohammed bin Salman's initial target of $2 trillion. 

Aramco said it would sell 1.5% of the company in a blockbuster initial public offering worth $24-25.6 billion, , scaling down Saudi Arabia's original plan to sell up to 5% of the firm.

"The base offer size will be 1.5% of the company's outstanding shares," the state-owned energy giant said as it began taking bids from investors in a price range of 30-32 Saudi riyals per share ($8-8.5). 

The much-delayed offering is a cornerstone of de facto ruler Prince Mohammed's ambitious plan to diversify the oil-reliant economy.

It could exceed the world's biggest listing - the $25 billion float of Chinese retail giant Alibaba in 2014. 

But the plans are a long way from the crown prince's initial aim to raise as much as $100 billion from a dual listing - a first flotation of 2% on the kingdom's Tadawul bourse, followed by a further 3% on an overseas exchange. 

The firm has said there are no current plans for an international stock sale and the IPO seems to be banking on local demand, with one-third of the offering reserved for Saudi retail investors. 

Aramco kicked off its investor road show yesterday, but a source close to the company told AFP it will not be marketing the shares overseas, including the US, as originally planned. 

The source did not offer an explanation but analysts said it was because the listing was not compatible with US regulatory requirements. 

Aramco has also shied away from plans to list on foreign exchanges such as New York owing to litigation risks. 

The launch has been dogged by delays since the idea was first announced in 2016, with Prince Mohammed's desired valuation of $2 trillion meeting with scepticism from investors and analysts.

Tarek Fadlallah, chief executive officer of the Middle East unit of Nomura Asset Management, called the company's valuation of between $1.6-1.71 trillion a "sensible compromise".

If priced at the top end of the range, it could eclipse Alibaba to become the world's biggest IPO, Fadlallah added on Twitter.