Lyse Doucet reports on the long queues at Egyptian polling stations
Votes are being counted in Egypt after a high turnout in the first leg of a referendum on a new constitution.
President Mohammed Morsi and his Muslim Brotherhood have endorsed the document, but critics say it is poorly drafted and favours Islamists.
Violent incidents were reported during voting, but not the widespread clashes that preceded the poll.
Early indications suggested that a majority of those who have voted so far may have backed the document.
A Muslim Brotherhood official told Reuters news agency that Egyptians had narrowly voted in favour of the draft constitution in the first round, according to the party's unofficial tally.
Opposition officials were also quoted as saying the "yes" vote appeared to be ahead.
At the scene
Most observers believe that, whatever the strength of feeling on each side of the argument, the Muslim Brotherhood is better organised, and so more likely to win.
One unknown factor is the view of harder-line Islamists, such as the Salafists, who may possibly vote "No" because they believe the constitution does not contain a strong enough commitment to Islamic values.
What seems most likely is that this referendum will not end this debate, a fundamental argument over Egypt's future, particularly if the outcome is as close as many expect.
Egyptians have got used to expressing their feelings about their country, in the strongest possible manner, and they are not about to stop.
Official results are not expected until after the second round next Saturday.
Rights groups fearsThe simple ballot paper asks voters to either endorse or oppose the new constitution.
Saturday's vote was held in Cairo, Alexandria and eight other provinces, a week before the rest of the country. Voting was extended by four hours because of the high turnout.
Polling reportedly had to be spread out because few judges were willing to supervise the referendum.
Human rights groups have expressed fears that the results from the first round could sway the opinion of those voting in the second.
A constitution must be in place before elections can be held early next year.
Mr Morsi was elected president in June with just over half of the vote, more than a year after Hosni Mubarak was overthrown in a popular revolt in Egypt, the most populous country in the Arab world.
Opponents of the new constitution include liberals and others who want a more secular future for Egypt.
They say the charter would take away some of the new freedoms won in last year's revolution.
The opposition National Salvation Front had vehemently opposed the referendum, but this week said its supporters should go to the ballot boxes to vote "No".
On Saturday it expressed "deep concern... over the number of irregularities and violations in the holding of the referendum".
Supporters of the draft constitution have accused the opposition of sowing "lies and discord".
'Deep concern'During the first round of voting the headquarters of the opposition al-Wafd party in Cairo was attacked, reportedly by extremist Islamists.
Clashes were also reported in the cities of Dakahlia and Alexandria.
The violence in Alexandria reportedly broke out after a cleric at a mosque urged worshippers to vote "Yes".
It continued late into the evening, with police firing tear gas, and at least 15 people injured in the fighting.
But BBC Arabic reporters outside Cairo said the situation was mostly calm
The Egyptian army's chief of staff, Gen Sedky Sobhi, told the BBC he was satisfied with the situation inside and outside polling stations.
Some 250,000 security personnel have been deployed to safeguard a referendum in which more than 51 million people are registered to vote overall.
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