The Egyptian Telecommunications Ministry has asked local internet users to limit the amount they download so that businesses are not crippled by lack of access.
Two of the three submarine cables that handle web traffic for the country were damaged earlier this week, leaving all data to go via the remaining cable.
No explanation has been given for the breakdown, which is now expected to take two weeks to fix.
"People who download music and films are going to affect businesses which have more important things to do," ministry spokesman Mohammed Taymur told Agence France-Presse.
Asked whether pornographic movies account for much internet traffic to Egypt, Taymur said: "That's another matter. Everyone downloads what they want. You can't forbid people from downloading certain movies."
The outage has caused huge problems for Egypt's call centre industry, which the ministry estimates is currently running at a third of normal capacity. Meanwhile, up to 70 per cent of internet activity in the rest of the country is being curtailed.
Analyst firm Gartner has suggested that the companies are being affected because of poor disaster planning. Most plans allow only for a week's shutdown, but if repairs take longer serious losses will be incurred.
"The impact of a disaster that lasts more than a week can have an enormous negative impact on revenue, reputation and brand," said Roberta Witty, research vice president at Gartner.
"Regional incidents, service provider outages, terrorism and pandemics can easily last longer than seven days.
"Organisations must be prepared. More mature business continuity management and disaster recovery programmes plan for outages of at least 30 days."
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