Hundreds of thousands of Egyptians have poured into Cairo's Tahrir Square for the latest protest calling for Hosni Mubarak's government to step down.
Correspondents say it is the biggest demonstration since the protests began on 25 January.
It comes despite the government's announcement of its plans for a peaceful transfer of power.
President Mubarak has said he will stay until elections in September.
In Tahrir Square, attempts by the army to check the identity cards of those joining the demonstration were abandoned because of the sheer weight of numbers.
Our correspondent says the message to the authorities is simple - there is huge support from all walks of Egyptian life for the protests, and the government's concessions are not enough.
Wael Ghonim, a Google executive was detained and blindfolded by state security forces for 12 days, was feted by the crowds as he entered Tahrir Square.
He is credited with setting up the page on the Facebook social network that helped galvanise protesters.
"We will not abandon our demand and that is the departure of the regime," Mr Ghonim told protesters in the square, to cheers and applause.
Referring to the protesters who have died in clashes with the security forces, he said: "I'm not a hero but those who were martyred are the heroes."
This latest demonstration in Cairo, as the protests enter their third week, came as large crowds demonstrated in the second city, Alexandria, and other Egyptian towns and cities.
The protesters are continuing to call for Mr Mubarak to leave office immediately, and say they are sceptical about any transition managed by the government.
In his response to the protests, President Mubarak has set up a committee to propose constitutional changes, and another is being formed to carry the changes out.
Vice-President Omar Suleiman, who announced the formation of the new committees, said he had briefed Mr Mubarak on recent talks with the opposition, and the president had welcomed the process of "dialogue" and "national reconciliation".
"The president also underlined the importance of continuing [the process] and moving from guidelines to a clear map with a definite timetable" for a "peaceful and organised" transfer of power, he said.
Among the key expected changes are a relaxation of presidential eligibility rules, and the setting of a limit for presidential terms.
A third committee, expected to begin its work in the next few days, would investigate clashes between pro- and anti-Mubarak groups last week and refer its findings to the prosecutor-general, Mr Suleiman said.
He also said President Mubarak had issued directives to stop repressive measures against the opposition.
Meanwhile, US Vice-President Joe Biden urged Mr Suleiman to make an orderly transition of power in Egypt that is "prompt, meaningful, peaceful and legitimate", the White House said.
During a telephone call, Mr Biden also urged the immediate lifting of Egypt's emergency laws.
The BBC's Yolande Knell reports that some of the protesters in Tahrir Square concede that plans to make constitutional changes - which the opposition has long called for - are a positive step, but others are sceptical about Mr Suleiman's intentions.
"We don't trust them any more," Ahmed, one young Egyptian queuing to get into the square, told the BBC. "How can Suleiman guarantee there'll be no more violence around the election after all the attacks we've seen on young people."
A middle-aged protester, Mustafa, said: "We are asking why there is no committee for young people. He has to ask the young people what they want - this is all about the young people."
The unrest over the last two weeks has seen fierce clashes with police, and pitched battles between protesters and Mubarak supporters.
Human Rights Watch (HRW) researchers say they have confirmed the deaths of 297 people since 28 January, based on a count from seven hospitals in the cities of Cairo, Alexandria and Suez. No comprehensive death toll has been given by the Egyptian government.
Some economic activity has resumed, but authorities have delayed reopening the stock exchange until Sunday. On Friday it was estimated that the paralysis resulting from the unrest had been costing the economy an average of $310m (£193m) a day.
The number of those on Tahrir Square has been swelling each day and dropping back overnight.
Meanwhile, leaked US diplomatic cables carried on the Wikileaks website have revealed that Mr Suleiman was named as Israel's preferred candidate for the job after discussions with American officials in 2008.
As Egypt's intelligence chief, he is said to have spoken daily to the Israeli government on issues surrounding the Hamas-run Gaza Strip via a secret "hotline".