Overnight clashes in Cairo between supporters and opponents of Egypt's Islamist leader have killed at least five people, according to state television.
Street battles raged outside the presidential palace as the nation descended further into political turmoil over the constitution drafted by president Mohammed Morsi's allies.
It was the worst violence since Egypt's latest crisis erupted on November 22, when Mr Morsi assumed near absolute powers.
It was also the first time supporters of rival camps had fought each other since last year's uprising that toppled authoritarian ruler Hosni Mubarak.
State television quoted the health ministry as saying five people were killed and 446 were injured as mobs battled each other with firebombs, rocks and sticks outside the presidential complex in the Heliopolis district of the capital.
The fighting erupted late yesterday when thousands of Mr Morsi's Islamist supporters descended on an area near the presidential palace where 300 opponents were staging a sit-in.
The Islamists, members of Mr Morsi's Muslim Brotherhood, chased the protesters away from their base outside the palace's main gate and tore down their tents.
After a brief lull, hundreds of opponents arrived and began throwing firebombs at the president's backers, who responded with rocks.
The crowds swelled and the clashes continued well after nightfall, spreading from the immediate vicinity of the palace to residential streets nearby.
The deployment of hundreds of riot police did not stop the fighting. The officers later fired tear gas to disperse Mr Morsi's opponents. Volunteers ferried the wounded on motorcycles to waiting ambulances, which rushed them to hospitals.
By dawn, the violence had calmed, but both sides appeared to be digging in for a long struggle, with the opposition vowing more protests later today and rejecting any dialogue unless the charter is rescinded.
Mr Morsi seems to be pressing relentlessly forward with plans for a December 15 constitutional referendum to pass the new charter.
The large scale and intensity of the fighting marked a milestone in Egypt's rapidly entrenched schism, pitting the Brotherhood and ultra-conservative Islamists in one camp against liberals, leftists and Christians in the other.
The violence spread to other parts of the country yesterday.
Anti-Morsi protesters stormed and set ablaze the Brotherhood offices in Suez and Ismailia, east of Cairo, and there were clashes in the industrial city of Mahallah and the province of Menoufiyah in the Nile Delta north of the capital.
There were rival demonstrations outside the Brotherhood's headquarters in the Cairo suburb of Moqatam, and in Alexandria security officials said senior Brotherhood official Sobhi Saleh was taken to hospital after being severely beaten by Morsi opponents.
Mr Saleh, a former MP, played a key role in drafting the disputed constitution.
Compounding Morsi's woes, four of his advisers resigned yesterday, joining two other members of his 17-member advisory panel who have abandoned him since the crisis began.
The opposition is demanding he rescind the decrees giving him nearly unrestricted powers and shelve the controversial draft constitution, which the president's Islamist allies rushed through last week in an all-night session shown live on state TV.
Mohamed ElBaradei, a leading opposition reform advocate, said late yesterday that Mr Morsi's rule was "no different" to Mubarak's.
"In fact, it is perhaps even worse," the Nobel Peace Prize laureate told a news conference after he accused the president's supporters of a "vicious and deliberate" attack on peaceful demonstrators outside the palace.
"Cancel the constitutional declarations, postpone the referendum, stop the bloodshed, and enter a direct dialogue with the national forces," he wrote on his Twitter account, addressing Mr Morsi.