Uber Technologies Inc's conservative initial public offering (IPO) could not keep its shares from sinking in their trading debut on Friday, fuelling debate on Wall Street over whether the outcome of the most anticipated listing since Facebook Inc would weigh on other Silicon Valley unicorns.

Key points: Uber's shares were down by 7.6 per cent at the end of the day

Uber's shares were down by 7.6 per cent at the end of the day The company's chief executive says shareholders will be rewarded as Uber continues to build

The company's chief executive says shareholders will be rewarded as Uber continues to build Only about a fifth of IPOs ended their first day of trading in the red in the past two years

Uber chief executive Dara Khosrowshahi, who was on the trading floor to mark the debut, tried to calm investors by pointing to the company's growth prospects and expansion plans.

"My reaction [to the share price] is if we build and build well, shareholders will be rewarded," Mr Khosrowshahi told Reuters.

"We're certainly not measuring our success over a day, it really is over the years."

The IPO was a watershed moment for the decade-old company, which was started after its founders struggled to find a cab on a snowy night.

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Uber considered going public for at least four years.

Yet the ride-hailing company picked a rough week for its IPO — plagued by market turbulence fuelled by US-China trade worries.

Moreover, smaller rival Lyft Inc's shares plunged this week after its first earnings as a public company.

Uber was the biggest of a group of Silicon Valley start-ups that have spent years raising money in private rounds at record prices.

Many of these companies are now looking to follow with their own IPO.

Some, like Uber and Lyft, are unprofitable.

Uber's shares ended the day down 7.6 per cent at $US41.57, even as the S&P 500 reversed losses to end in positive territory.

Only about a fifth of IPOs have ended their first day of trading in the red in the past two years, according to Dealogic data.

Uber's shares ended the day down 7.6 per cent. ( AP: Mark Lennihan )

Low pricing did not prevent plunge

Uber priced its IPO on Thursday at the low end of its targeted range, hoping that approach would spare it the trading plunge suffered by Lyft.

Lyft ended down 6.9 per cent on Friday, and is 28 per cent below its IPO price.

Uber had already lowered its valuation expectations twice in the past two months to address investor concerns over its mounting losses.

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Marred by scandal

The company's road to IPO was marred by several hurdles including increased regulation in several countries and fights with its drivers over wages.

Uber has also weathered controversies including revelations of a culture of sexism and bullying at Uber and US Department of Justice investigations.

After a series of embarrassments, Mr Kalanick was forced to resign in 2017 by a group of investors.

Uber then hired Mr Khosrowshahi to lead the company.

Uber has said it has the potential to grow not just in the cab-hailing business, but also as a "superapp" to provide logistic services, such as grocery and food delivery, organising freight transportation, and even financial services, much like Grab, its South-East Asian counterpart.

But market experts have struggled to find value in a company that has consistently posted losses, and warned that it may never be profitable.

Uber board member Ryan Graves, right, rings the ceremonial bell. ( AP: Richard Drew )

Reuters