The scale of Egypt's crackdown on the Internet and mobile phones amid deadly protests against the rule of President Hosni Mubarak is unprecedented in the history of the web, experts said.
US President Barack Obama, social networking sites and rights groups around the world all condemned the moves by Egyptian authorities to stop activists using cellphones and cybertechnology to organise rallies.
"It's a first in the history of the Internet," Rik Ferguson, an expert for Trend Micro, the world's third biggest computer security firm, told AFP.
Julien Coulon, co-founder of Cedexis, a French Internet performance monitoring and traffic management system, added: "In 24 hours we have lost 97 per cent of Egyptian Internet traffic.
According to Renesys, a US Internet monitoring company, Egypt's four main Internet service providers cut off international access to their customers in a near simultaneous move at 2234 GMT on Thursday.
Around 23 million Egyptians have either regular or occasional access to the Internet, according to official figures, more than a quarter of the population.
"In an action unprecedented in Internet history, the Egyptian government appears to have ordered service providers to shut down all international connections to the Internet," James Cowie of Renesys said in a blog post.
Link Egypt, Vodafone/Raya, Telecom Egypt and Etisalat Misr were all off air but Cowie said one exception was the Noor Group, which still has 83 live routes to its Egyptian customers.
He said it was not clear why the Noor Group was apparently unaffected "but we observe that the Egyptian Stock Exchange (www.egyptse.com) is still alive at a Noor address."
Mobile telephone networks were also severely disrupted in the country on Friday. Phone signals were patchy and text messages inoperative.
British-based Vodafone said all mobile operators in Egypt had been "instructed" Friday to suspend services in some areas amid spiralling unrest, adding that under Egyptian law it was "obliged" to comply with the order.
Egyptian operator ECMS, linked to France's Telecom-Orange, said the authorities had ordered them to shut them off late Thursday.
"We had no warning, it was quite sudden," a spokesman for Telecom-Orange told AFP in France.
The shutdown in Egypt is the most comprehensive official electronic blackout of its kind, experts said.
Links to the web were were cut for only a few days during a wave of protests against Myanmar's ruling military junta in 2007, while demonstrations against the re-election of Iranian president Mahmoud Ahmadinejad in 2009 specifically targeted Twitter and Facebook.
Egypt -- like Tunisia where mass popular unrest drove out Zine El Abidine Ben Ali earlier this month -- is on a list of 13 countries classed as "enemies of the Internet" by media rights group Reporters Without Borders (RSF).
"So far there has been no systematic filtering by Egyptian authorities -- they have completely controlled the whole Internet," said Soazig Dollet, the Middle East and North Africa specialist for RSF.
Condemnation of Egypt's Internet crackdown has been widespread.
Obama and Secretary of State Hillary Clinton called on Cairo to restore the Internet and social networking sites.
Facebook, the world's largest social network with nearly 600 million members, and Twitter also weighed in.
"Although the turmoil in Egypt is a matter for the Egyptian people and their government to resolve, limiting Internet access for millions of people is a matter of concern for the global community," said Andrew Noyes, a Facebook spokesman.
Twitter, which has more than 175 million registered users, said of efforts to block the service in Egypt: "We believe that the open exchange of info & views benefits societies & helps govts better connect w/ their people."
US digital rights groups also criticised the Egyptian government.
"This action is inconsistent with all international human rights norms, and is unprecedented in Internet history," said Leslie Harris, president of the Center for Democracy and Technology in the United States.