Facebook chief executive Mark Zuckerberg today faced a tougher, tenser grilling at his second congressional hearing, as lawmakers unleashed a litany of complaints about the company's privacy practices, its failure to fight the opioid crisis and the lack of diversity within its executive ranks.

For five hours, Democrats and Republicans on the House Energy and Commerce Committee took turns swiping at Zuckerberg, holding him to "yes" and "no" questions and frequently cutting him off - a tactic that at times appeared to frustrate the Facebook co-founder.

Facebook's data practices were the official topic of the hearing, prompted by its entanglement with Cambridge Analytica, a political consultancy that improperly accessed 87 million Facebook users' names, "likes" and other personal information. At one point in the hearing, Zuckerberg acknowledged that his own data had been accessed by Cambridge Analytica.

Read more: Zuckerberg's own data was sold to 'malicious third parties'


Even as he apologised for the mishap and other recent troubles at Facebook, however, lawmakers repeatedly expressed doubt that the social giant could fix its troubles on its own - and threatened to regulate the company and its tech industry peers.

Opening the session, the House panel's leader, Republican Greg Walden, called Facebook an "American success story." But he added: "While Facebook has certainly grown, I worry it has not matured. I think it is time to ask whether Facebook may have moved too fast and broken too many things."

For Facebook, the Cambridge Analytica crisis has triggered unprecedented political scrutiny, prompting Zuckerberg to testify at two hearings in two days, spanning 10 hours of questioning from 91 lawmakers. Meanwhile, the company could soon face major fines from the Federal Trade Commission, which has opened an investigation.

But Facebook's political and legal challenges span more than Cambridge Analytica. In the wake of its review of the firm's activities, Facebook also has acknowledged that malicious actors scraped information from the public profiles of practically its entire base, more than 2 billion users.

For weeks, the revelations have wreaked havoc on Facebook's stock, wiping out billions of dollars in value. On Wednesday, though, it closed up 0.8 percent, continuing its rebound this week.

Zuckerberg started the House hearing by repeating the same apology he gave to the Senate a day earlier. "It was my mistake, and I'm sorry. I started Facebook, I run it, and I'm responsible for what happens here," he told House lawmakers.

But Zuckerberg's demeanour vacillated between calm and frustrated as lawmakers challenged the 33-year-old billionaire on a host of issues beyond consumer privacy. He sipped from a cup frequently as lawmakers hammered him with grievances.

Democratic representive G.K. Butterfield demanded that Zuckerberg improve the company's hiring practices, pointing out that Facebook had no people of colour in its highest executive ranks. Republican representative Joe Barton pressed Zuckerberg to address conservatives' fears that the site censors their content, news and views. And Republican David McKinley accused Zuckerberg and Facebook of "hurting people" by failing to thwart those who try to sell opioids on the site.

"I think there are a number of areas of content we need to do a better job of policing on our service," Zuckerberg replied.

Some lawmakers read letters from their constituents, detailing common complaints about the service that more than 200 million Americans use. In one of the toughest exchanges on Wednesday, Democratic Representative Anna Eshoo - a lawmaker who represents a slice of Silicon Valley - needled Zuckerberg for failing to explain its data-collection practices to users in "clear and pedestrian language."

Her Democratic colleague, New Mexico Representative Ben Lujan, raised reports that Facebook collects data on those who aren't even users - called "shadow profiles" by some. Zuckerberg, however, said he was "not specifically familiar with that."

And Lujan pointed to researchers who had publicly expressed fears that Facebook data could be scraped by malicious actors, emphasising that the tech giant should have terminated its phone and email lookup feature sooner than it did.

"Facebook knew about this in 2013 and 2015, but you didn't turn the feature off until Wednesday of last week," he said. "This is essentially a tool for these malicious actors to steal a person's identity and put the finishing touches on it."

Republican Representative Marsha Blackburn meanwhile remarked that Facebook looks "a whole lot like the Truman Show," where users' information is "made available to people they don't know, and then that data is crunched and used and they are fully unaware of this."

The Tennessee lawmaker cited rules that govern health data, financial transactions and other industries, before touting her bill that would require tech companies to obtain user permission before they can collect and sell user data. Facebook has long lobbied against the so-called Browser Act.

Once the hearing concluded, lawmakers like Walden said they hoped to invite other tech executives to testify - a sign that scrutiny could intensify and widen to cover companies like Google and Twitter.

"If all we do is have a hearing and nothing happens, then that's not accomplishing anything," said New Jersey Rep. Frank Pallone, the top Democrat on the House Energy and Commerce Committee.

- Washington Post