Amr Moussa and Ahmed Shafiq traded accusations, saying false rumours were being spread that each was about to withdraw from the hotly contested race.

Other candidates have also been accused of breaking “election silence” rules.

Counting has begun at some polling stations following Egpyt’s first free presidential polls.

The elections pit Islamists against secularists, and revolutionaries against Mubarak-era ministers.

In all, 13 candidates are running. The front-runners are:

Ahmed Shafiq, a former commander of the air force and briefly prime minister during February 2011 protests

Amr Moussa, who has served as foreign minister and head of the Arab League

Mohammed Mursi, who heads Muslim Brotherhood’s Freedom and Justice Party

Abdul Moneim Aboul Fotouh, an independent Islamist candidate

A run-off vote is scheduled for 16 and 17 June if no candidate manages to get more than 50% of the votes in the poll, in which 50 million people are eligible to vote.

But no clear picture is likely to emerge until Tuesday, when they are announced in full.

A row erupted between two of the main candidates for apparently spreading damaging rumours about each other.

In a BBC interview, Mr Moussa launched an angry attack on his rival Mr Shafiq – who was appointed prime minister in the dying days of Mr Mubarak’s rule – saying he represented the ideas of the old regime.

Mr Moussa denied what he described as “sinister rumours” that he was about to withdraw from the race.

But in later interviews Mr Shafiq hit back, accusing Mr Moussa’s campaigns of spreading similar rumours – and pointing out Mr Moussa’s connections to the old regime. Mr Moussa served as a minister under Mubarak from 1991 to 2001.

Mr Shafiq, Mr Fotouh and Mr Mursi have all been accused of breaking rules requiring candidates keep silent on polling days and on Wednesday the election commission said it would be investigating such allegations.

Turnout appeared to vary across the country on Thursday, which authorities had declared a public holiday.

In Cairo, there were long queues at some polling stations but elsewhere, such as Alexandria and Suez, there were reports of slow voting.

Egypt’s election commission estimated that about 50% of eligible voters had participated, reported official news agency Mena.

NGOs and rights groups monitoring the election have reported some complaints, including illegally campaigning outside polling stations.

But election observers said in general the vote appeared to have passed off successfully.

“We still have to see whether all the procedures were fair,” said former US congresswoman Jane Harman, an international observer.

“But as one observer of other elections like Tunisia, I must say that this process for the last five days since I have been in Egypt was enormously impressive and a tribute to the people of Egypt.”

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