There is no internet traffic going in or out of Egypt, a major service provider for the country says.
Bloomberg reported Italian-based Seaborne's claim that all web traffic had ceased at around 12.30AM local time.
Mobile phone text messaging appeared to be down, hours before activists who used both to organise large anti-government protests planned further actions, AFP reported.
Reports also said the government had stepped security up a notch, sending the country's anti-terror team onto the streets.
The interior ministry had said in a statement late on Thursday it would take "decisive measures" against dissidents who planned protests after Friday noon prayers, saying the activists "sent messages to citizens to gather in a number of mosques in the provinces during Friday prayers".
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Tens of thousands protested around the country on Tuesday in the largest anti-government demonstrations in decades.
The protests continued on Wednesday and Thursday, killing five demonstrators and two policemen in clashes.
Mobile phone services went down on Tuesday in a downtown Cairo area where most of the protesters were gathered, and the social networking site Twitter said its services were also blocked that day.
In Cairo, internet users said they could not access the web, with some saying access was slow and intermittent, starting late on Thursday.
Text messaging was also unavailable.
