Tens of thousands of people have converged on the heart of Cairo, responding to a call for a million Egyptians to unite in the largest protest in a week of unceasing demands for President Hosni Mubarak to leave after nearly 30 years in power.
A stream of protesters arrived in Tahrir Square (Liberation Square) at checkpoints guarded by protesters and the army, which has promised that it would not fire on protesters.
The announcement was a sign that army support for Mr Mubarak may be unravelling as momentum builds for an extraordinary eruption of discontent and demands for democracy in the United States' most important Arab ally.
"We are not going anywhere until Mubarak leaves," said Mohammed Abdullah, a 27-year-old aviation engineer.
Mr Mubarak would be the second Arab leader pushed from office by a popular uprising in the recent history of the modern Middle East.
The loosely organised and disparate movement to drive him out is fuelled by deep frustration with an autocratic regime blamed for ignoring the needs of the poor and allowing corruption and official abuse to run rampant.
After years of tight state control, protesters emboldened by the overthrow of Tunisia's president took to the streets on January 25 and mounted a relentless and once unimaginable series of protests across this nation of 80 million people - the region's most populous country and the centre of Arabic-language film-making, music and literature.
The protests appeared to be better organised than earlier in the week. Volunteers wearing tags reading "Security of the People" said they were watching for government infiltrators who might try to instigate violence. "We will throw out anyone who tries to create trouble," one announced over a loudspeaker.
Authorities shut down all roads and public transport to Cairo, security officials said. Train services nationwide were suspended for a second day and all bus services between cities were halted. All roads in and out of the flashpoint cities of Alexandria, Suez, Masnoura and Fayoum were also closed.
The protesters - and US President Barack Obama's administration - roundly rejected Mr Mubarak's announcement on Monday of a new government which dropped his highly unpopular interior minister, who heads police forces and has been widely denounced by the protesters.