London's decision to deny Uber a license has produced howls of protest from jilted fans and wild cheers from critics.

Twitter (TWTR) and Facebook (FB) were flooded with comments after the decision was announced on Friday. Text messages flew between friends and tabloid editors prepared to blast the news across their front pages.

"UBER AND OUT!" read the headline on London's Evening Standard.

Transport for London sent shock waves through the capital city Friday morning, announcing that it would not renew Uber's license because of concerns over its approach to reporting serious crimes and other issues.

Uber, which has 21 days to appeal the ruling, quickly blasted an email to users asking them to sign an online petition that pleads with London's mayor to "save" the app. It received over 181,000 signatures in about four hours.

"I don't believe black cabs should run London like a cartel," wrote Uber fan James Pace, who posted his message alongside the petition. "If Uber has problems, let's resolve them not just ban them."

Related: London says it won't renew Uber's license

Uber, which has been used by 3.5 million Londoners, has developed a loyal fan base by offering convenience and lower prices than traditional "Black Cabs." It has 40,000 licensed drivers in the city.

Londoners acknowledge there are problems at Uber, but many were panic stricken at the idea of the service shutting down. Some argued that cutting off Uber would even be dangerous.

"Losing #Uber makes London more unsafe for young people, especially students who can't afford the ridiculous rates of Black Cabs," wrote Twitter user Lauren Powell‏, who lives in a commuter town on the outskirts of London.

Anger was also directed at mayor Sadiq Khan, who said he "fully supports" the move by Transport for London.

"[This] decision is a bombshell for Uber drivers," said Twitter user Duncan Scott. "Sadiq Khan doesn't even acknowledge the jeopardy they're now in."

One Uber driver, Papy Bola, told CNNMoney that he wasn't sure what he'd do for work if the app was shut down.

"There's nothing wrong with Uber. You work, no stress, you get your fee, they get their commission. That's it," he said, adding that he feels safe in an Uber because thieves know users typically pay with credit cards instead of cash.

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But not everyone took Uber's side. Critics added to the online conversation by arguing that Uber should live up to British business standards.

"It's perfectly possible to run a taxi company without treating drivers poorly or cutting corners on safety. Uber's fate is of its own making," tweeted Frances O'Grady, general secretary of the Trades Union Congress.

It's perfectly possible to run a taxi company without treating drivers poorly or cutting corners on safety. Uber's fate is of its own making — Frances O'Grady (@FrancesOGrady) September 22, 2017

Steve Garelick, a union official who represents Black Cabs, had been campaigning to halt Uber's advances in London. But he described the victory as "bittersweet," saying he worried about Uber drivers losing their jobs.

"I sympathize that people won't be getting cheap journeys in the future," he said. "But the reality is that [customers] have got to pay the price. It's as simple as that."

-- Susie East and Muhammad Darwish contributed to this report.