JOIN USMany mosques in the capital shut down a move unprecedented for Friday, the Muslim day of prayer as worshippers and clerics streamed to the square outside Sanaa University.
Protesters filled the plaza and spilled out along three adjoining streets. Previous demonstrations have taken up the square and at most two of the streets that feed into it.
The demonstrators set up tents and hung up posters of young men who were fatally shot by government forces during previous protests.
The opposition said it hoped to have 1 million people on the streets today to press for President Ali Abdullah Saleh's ouster after 32 years in power.
Today evening, two local newspaper reporters and a television cameraman were detained by security forces, according to Gamal Anaam, member of the Yemeni journalists' union. A security official declined to comment.
Saleh escalated his confrontation with the rapidly expanding uprising a week ago, taking on emergency powers that give him a freer hand to quell protests.
Parliament, which is packed with his supporters, passed a 30-day state of emergency that suspends the constitution, bars protests and gives security forces far-reaching powers of arrest.
Saleh has been hit by a wave of defections by military commanders, ruling party members and others, swelling the ranks of the opposition and leaving him isolated.
In a failed attempt to appease the protesters, he offered not to run again when his current term ends in 2013. He then offered to step down by the end of this year and open a dialogue with the leaders of the demonstrators.
Protesters rejected all his offers, furious after his security forces shot dead more than 40 demonstrators in Sanaa last month.
Today, there were anti-Saleh protests in at least 14 other provinces around the country. Witnesses said hundreds of thousands of people attended demonstrations in the provinces of Aden, Taaz, and Hadramout.
The Sanaa crowd was supported by soldiers with anti-aircraft guns and Kalashnikov rifles, who set up half a dozen checkpoints around the square to prevent intrusions by president's loyalists.
Protesters, who have called for a "Friday of Salvation," raised black cards while chanting "Ali Leave!" Women and children, their faces painted in the colours of the Yemeni flag, or the word "Leave," joined the protests.