Tens of thousands of Egyptian protesters surged around the presidential palace today and the opposition rejected President Mohammed Mursi's call for dialogue to end a crisis that has polarised the nation and sparked deadly clashes.

The Islamist leader's deputy said he could delay a 15 December referendum on a constitution that liberals opposed.

However, the concession only partly meets a list of opposition demands that include scrapping a decree that expanded Mr Mursi's powers.

"The people want the downfall of the regime" and "Leave, leave," crowds chanted after bursting through barbed wire barricades and climbing on tanks guarding the palace of Egypt's first freely elected president.

Their slogans echoed those used in a popular revolt that toppled Mr Mursi's predecessor Hosni Mubarak in February 2011.

Vice President Mahmoud Mekky said in a statement sent to local media that the president was prepared to postpone the referendum if that could be done without legal challenge.

The dialogue meeting is expected to go ahead tomorrow in the absence of most opposition factions.

"Tomorrow everything will be on the table," a presidential source said of the talks.

The opposition has demanded that Mr Mursi rescind a 22 November decree giving himself wide powers.

They are also seeking a delay to the vote set for 15 December on a constitution drafted by an Islamist-led assembly which they say fails to meet the aspirations of all Egyptians.

The state news agency reported that the election committee had postponed the start of voting for Egyptians abroad until Wednesday, instead of tomorrow as planned.

It did not say whether this would affect the timing of voting in Egypt.

Ahmed Said, leader of the liberal Free Egyptians Party, told Reuters that delaying expatriate voting was made to seem like a concession but would not change the opposition's stance.

He said the core opposition demand was to freeze Mr Mursi's decree and "to reconsider the formation and structure of the constituent assembly", not simply to postpone the referendum.

The opposition organised marches converging on the palace.

Elite Republican Guard units had ringed with tanks and barbed wire yesterday after violence between supporters and opponents of Mr Mursi killed seven people and wounded 350.

Islamists, who had obeyed a military order for demonstrators to leave the palace environs, held funerals today at Cairo's al-Azhar mosque for six Mursi partisans who were among the dead.

In a speech late last night, Mr Mursi refused to retract his 22 November decree or cancel the referendum on the constitution, but offered talks on the way forward after the referendum.

The National Salvation Front, the main opposition coalition, said it would not join the dialogue.

The Front's coordinator, Mohamed ElBaradei, a Nobel peace laureate, dismissed the offer as "arm-twisting and imposition of a fait accompli".