Tens of thousands packed Tahrir Square on Tuesday to protest a power grab by Mohamed Morsi, piling pressure on Egypt's Islamist president as he faces his most divisive crisis since taking power in June.
The huge turnout in the iconic square in the heart of Cairo, as well as in the Mediterranean city of Alexandria and most of Egypt's 27 provinces, marked the largest mobilisation yet against the president.
Elsewhere in the country, protesters enraged by Morsi's decision to grant himself sweeping powers attacked three regional headquarters belonging to the president's Muslim Brotherhood movement, a security official said.
In Tahrir, protesters who had voted for Morsi in the election joined forces with die-hard opponents of the Islamist.
"I'm here to protest Morsi's autocratic decisions," said Mohammed Rashwan, an engineering graduate who voted for Morsi in the country's first presidential election since a popular uprising toppled Hosni Mubarak last year.
"I have discovered that he is pro-Muslim Brotherhood and not the revolution," Rashwan told AFP from the packed square.
Throughout the afternoon and into the evening, marches poured into Tahrir Square, swelling the numbers, amid an electrifying atmosphere many said reminded them of the 2011 uprising.
The protesters are angry at the decree that Morsi announced last Thursday allowing him to "issue any decision or law that is final and not subject to appeal", which effectively placed him beyond judicial oversight.
The decree put him on a collision course with the judiciary and consolidated the long-divided opposition which accuses him of taking on dictatorial powers.
The demonstrations come a day after Morsi stuck by his decree after a meeting with the country's top judges aimed at defusing the crisis.
"The solution is to cancel the constitutional declaration... We won't replace a dictator with another," said protester Asser Ayub, 23, waving an Egyptian flag.
In the Mediterranean city of Alexandria, thousands gathered in Qait Ibrahim square. The Muslim Brotherhood wrote on its Twitter account that it ordered its members to evacuate the group's headquarters after it came under attack.
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"Down with the rule of the Supreme Guide," the protesters shouted, in reference to Brotherhood leader Mohammed Badie, a chant echoed in the Red Sea resort of Sharm el-Sheikh, where hundreds took to the streets.
Protesters also stormed and ransacked the group's headquarters in the Nile Delta city of Mansura, a security official said, and attacked the Islamists' office in the city of Mahalla.
Three people have died in clashes since Morsi decreed his new powers on Thursday.
A rival rally in Cairo by the Muslim Brotherhood in support of the president was called off to "avoid potential unrest" but that has done little to abate the split between Morsi's supporters and foes.
After the meeting on Monday with top judges, Morsi stuck by his controversial decree.
There was "no change to the constitutional declaration," presidential spokesman Yasser Ali told reporters at the end of the meeting.
But he added Morsi sought to clarify that any irrevocable decisions apply only to issues related "to his sovereign powers" and stressed the temporary nature of the decree.
The head of the Freedom and Justice Party (FJP) -- the Brotherhood's political arm -- said the meeting between Morsi and the judges had been "fruitful".
But judges said the crisis was not over.
"The meeting failed," Judge Abdel Rahman Bahlul, who attended the talks, told the independent daily Al-Masry Al-Youm.
"We cannot say this is the end of the crisis between the judiciary and the presidency," another judge who attended the talks, Judge Ahmed Abdel Rahman, told the paper.
A judicial source told AFP that even if immunity were limited to sovereign powers, "which appears to be a compromise, there are still concerns that the text itself remains unchanged".
The decree bars the courts any from dissolving a controversial panel that is drafting a new constitution. Liberals, leftists and church leaders have already walked out of the Islamist-dominated panel charging that it fails to represent all Egyptians.