Protesters have ransacked the Cairo headquarters of president Mohammed Morsi’s Muslim Brotherhood Islamist group.
They stormed the six-storey building in an eastern Cairo district , leaving the heavily fortified villa with furniture and files on fire.
Smoke billowed out of the building’s smashed windows.
One protester removed the Muslim Brotherhood sign from the front wall.
The storming of the Brotherhood’s headquarters followed overnight clashes between armed Morsi supporters barricaded inside the building and young protesters pelting it with firebombs and rocks.
Activists say at least five protesters were killed in the violence.
It was not clear whether the Brotherhood supporters holed up inside who had been battling the protesters had fled the building.
Morsi critics view the Brotherhood headquarters as the seat of real power in Egypt, consistently claiming that the Islamist group’s spiritual leader, Mohammed Badie and his powerful deputy, Khairat el-Shater, were the ones actually calling the shots in the country, not the president.
The Brotherhood has in recent weeks fortified the building’s walls in anticipation of the massive opposition protests .
Meanwhile anti-Morsi protesters were gearing up for a second day of demonstrations.
Some protesters spent the night in dozens of tents pitched in the capital’s central Tahrir Square and in front of the president’s Ittihadiya Palace. They have vowed to stay there until Mr Morsi resigns. The president’s supporters, meanwhile, continued their sit-in in front of a major mosque in another part of Cairo.
The demonstrators are calling for widespread strikes in an attempt to ratchet up the pressure on the presiden.
Sunday’s protests were the largest seen in Egypt since the removal of Hosni Mubarak in February 2011.
Fears were widespread that the collisions between the two sides could grow more violent in coming days. Mr Morsi made clear that he would not step down and his Islamist supporters vowed not to allow protesters to remove one of their own.
Mr Morsi’s supporters have depicted the planned protest as a plot by Mubarak loyalists. But their claims were undermined by the extent of Sunday’s rallies. In Cairo and a string of cities in the Nile Delta and on the Mediterranean coast, the protests topped even the biggest ones of the 2011’s 18-day uprising, including the day Mubarak quit when giant crowds marched on Ittihadiya.
It is unclear now whether the opposition, which for months has demanded Mr Morsi form a national unity government, would now accept any concessions short of his removal. The anticipated deadlock raises the question of whether the army, already deployed on the outskirts of cities, will intervene.