Crowds are assembling in the centre of the Egyptian capital, Cairo, amid calls by protest leaders for a million people to rally in support of demands for the removal of President Mubarak.

Many Egyptians believe that Mr Mubarak's position has been fatally weakened after a declaration by the army last night that it will not use force against demonstrators. In a statement, the military described the people's demands as "legitimate."

The BBC's world affairs editor, John Simpson, told the programme that there was "a lot of excitement" in the city, adding that "this figure of a million is assuming mythic proportions... It represents a sign of popular power".

But he warned that mass enthusiasm of this kind "simply cannot endure for long" and that if the government decides to tough it out, "the people in the streets must be that much more determined".

"The most important thing," he said, "is that people who have been kept down for millennia... have shown they can take the city over" and that this sort of popular discontent "will spread throughout the middle east".

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