The Sri Lankan Government blocked access to social media platforms in the wake of explosions that killed more than 200 people on the holiest day of the Christian calendar.
The blasts, which targeted churches during Easter services and luxury hotels, also prompted the Government to impose an immediate nationwide curfew.
Officials said they ordered the social media blackout in an attempt to stop the viral spread of misinformation about the attacks online, a digital scourge that typically follows international news events and one that major tech giants long have struggled to curtail.
Already, researchers said they had seen a spike in false reports about the perpetrators and the number of victims in Sri Lanka, a country where regulators previously have accused sites, including Facebook, of serving as conduits for hate speech and worsening ethnic tensions.
But the temporary blockade on social media also sparked fresh concerns in the eyes of local residents and international observers that it would become harder for Sri Lankans to obtain accurate, timely information or communicate with loved ones, including those overseas.
"If I don't reply to your messages it is because WhatsApp and Facebook appears to have been shutdown in Sri Lanka," Colombo resident Roshni Fernando wrote on Twitter.
Talking to the Washington Post, Fernando said she grew up in London but recently moved to the Sri Lanka capital, one of the cities targeted in the attacks.
"People can now only communicate through SMS here, or Twitter I guess," said Fernando, explaining she was also unable to access YouTube and Instagram.
"I'm hearing reports that they've shut down Facebook and WhatsApp so that makes sense as I have had friends in London trying to contact me through both and I can't see them or message anybody on either Facebook or WhatsApp."
Announcing the move, Sri Lanka's Defence Ministry said that the "Government has taken steps to temporarily block all the social media avenues until the investigations are concluded."
One report from a state-run news service said "false news reports were spreading through social media" and the "blockage would be effective until investigations were concluded."
In a statement, Facebook said it is "working to support first responders and law enforcement as well as to identify and remove content which violates our standards," adding it is "committed to maintaining our services and helping the community and the country during this tragic time."
Representatives for Google-owned YouTube, Snapchat and Twitter did not respond to requests for comment.
Viber, a popular messaging app in Sri Lanka, did not comment on the block, but the platform tweeted soon after the attacks, offering support and encouraging users to "be responsible and rely on updates from official and trusted sources."
NetBlocks, a London-based digital rights organisation, said its data show each of those services had been affected. Alp Toker, its executive director, said he believed the Sri Lankan Government had ordered local internet providers to implement the blackout. The providers interpreted the order differently, explaining why some social-networking services still seemed to be operable for some users, he added.
Sanjana Hattotuwa, a senior researcher at Center for Policy Alternatives in Colombo who is monitoring social media for fake news, misinformation and incitement of hate or violence, said he had seen a significant uptick in false reports.
He said there is a significant amount of misinformation on the toll. Unverified information on perpetrators was spreading rapidly on Facebook and Twitter. He cited two instances of widely shared unverified information: One was an Indian media report attributing the attack to Muslim suicide bombers, and the other was a tweet from a Sri Lankan minister about an intelligence report warning of an attack.
Hattotuwa has asked users to flag such content directly to him. "There are new Twitter accounts popping up putting out unverified information. There are Facebook posts which violate the guidelines through either intent or are graphic in nature," he said. Hattotuwa is sharing the information with Facebook and Twitter, which he said are on "high alert."
Internet shutdowns aren't new to South Asia, which witnessed the highest number of shutdowns globally in 2018, according to a press freedom report by the Brussels-based International Federation of Journalists.
India topped the list, with 82 such instances, while Sri Lanka had one. The report said authorities justified most of these shutdowns by citing "law and order" imperatives, saying the measures were intended to preempt violence or were undertaken in response to it. There was, however, no "substantive" evidence to show that shutdowns can "scale down violence," the report said.
Around the world, though, governments have expressed deep unease with the spread of misinformation and violent acts on social media, particularly during major tragedies.
Facebook and YouTube, for example, struggled to remove graphic video from the deadly attack on two mosques in Christchurch last month. In response, the Government proposed new rules that would compel companies to take down such content faster or face penalties, an idea that European regulators also have considered in recent weeks.
Before yesterday, Sri Lanka's Government shut down access to social media platforms in March 2018 out of concerns that sites, including Facebook, had helped foment deadly ethic unrest in the deeply divided country. Anti-Muslim riots at the time left three dead and prompted leaders to declare a state of emergency.
In the aftermath, officials specifically identified Facebook and Facebook-owned WhatsApp as having "been used to destroy families, lives and private property." And they accused the tech giant of failing to act swiftly and aggressively enough to take down content that had been deemed a national security risk.
But Hattotuwa said Sri Lanka's action in 2018 yielded mixed results because it was undertaken too late, after the violence had already broken out.
"While a ban on social media helps to contain the spread of rumours, it also hampers efforts by journalists to push back on them," he said.