Protesters in Egypt have stormed the headquarters of the nation's ruling party, demanding the resignation of Muslim Brotherhood leader, Mohammed Morsi.
The Cairo building has been ransacked and burned, with the movement's leaders accusing security forces of failing to protect the headquarters. Staff had been evacuated earlier in the day.
Despite a day of violent riots in which at least seven people have been killed and hundreds injured, President Morsi has remained defiant.
Sunday marked the one-year anniversary of his inauguration but many are disillusioned with his rule and accuse him of failing to tackle security and economic problems.
Previously fragmented liberal and secular groups have been united under the banner of a grassroots movement called Tamarod (Rebellion).
A petition started by the group calling for a change in government has been signed by 22 million people, reports Sky news.
The crowds that gathered in Tahrir Square are some of the biggest since Hosni Mubarak was toppled in 2011. However in an interview with the Guardian, Morsi insisted there would be no second revolution like the Arab spring in 2011 that led to his appointment.
He said: "There is no room for any talk against this constitutional legitimacy. There can be demonstrations and people expressing their opinions.
"But what's critical in all this is the adoption and application of the constitution. This is the critical point."
The Egyptian military has said it will step in if violence spirals out of control.
US president, Barack Obama, urged "all parties to make sure they are not engaging in violence and that police and military are showing appropriate restraint".
Street fighting across the country that has caused several deaths and numerous injuries has preceded the protests.
An American, 21-year-old Andrew Pochter, was killed in Alexandria on Friday.