by Chris Bodenner
Scott Lucas updates:
Downtown Cairo is the scene of chaos right now with several buildings on fire - reports say.
1845 GMT: In Cairo, the ruling NDP's headquarters has been almost totally destroyed by the fire. Fire fighters are now trying to put out the flames after protesters destroyed the building. Reports suggest some protesters looted the building before it was set on fire.
1840 GMT: Rowya Rageh of Al Jazeera - Live from Alexandria - just reported that Army tanks can be found on the streets and are being welcomed by the protesters.
In the Sinai peninsula, tensions are rising in Sheikh Zuwayid where sporadic clashes continue. Unconfirmed reports suggest that some protesters have armed themselves and are fighting the security forces for control. Electricity to the city and most of the northern Sinai has been cut-off apparently.
1825 GMT: Sherine Tadros of Al Jazeera reports that flights into Cairo are being cancelled.