Stones were hurled at the party headquarters in Cairo as rioting and looting by anti-government protesters continued well into the night, in defiance of a curfew.
In a sign of the escalating clashes, the army was sent in for the very first time and military convoys were seen on the streets of Cairo.
President Hosni Mubarak imposed the city-wide curfew earlier to quell the violence, but this has now been relaxed to cover only Cairo, Alexandria and Suez.
According to medical officials, the number of dead stands at 5, with at least 850 injured, some with gunshot wounds.
As the tanks rolled into the streets to control the disorder, they were cheered on by the crowds.
Artillery fire was reportedly heard in central Cairo and thick smoke was also seen near parliament.