The Egyptian justice ministry said 27.1 per cent of registered voters took part.
Before it was amended the constitution stipulated that elections had to be supervised by judges, but Sabr said their task was made impossible by the number of polling stations and official interference.
"The head of the high election committee [the justice minister] issued instructions forbidding judges from touring the polling stations," he said.
"It is really sad to see Egypt - a republic - turned into a kingdom"
Be Humble, UK
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Sabr also cited cases in which polling stations observed by judges to have empty ballot boxes would suddenly be filled with votes when they returned an hour later.
Judicial oversight of elections has been reduced by the reforms.
Independent human rights groups and opposition parties also denounced the results of the referendum.
Hafez Abu Seada, the head of the Egyptian Organisation for Human Rights, said the official tally of "yes" votes might be correct but the turnout was suspect.
"Our organisation observed the referendum and our estimate for the people who voted ... is around 5 per cent for the whole day. So I doubt this is a true statistic," he told Reuters news agency.
The Hesham Mubarak Law Centre, an independent group co-ordinating observers, accused the ruling party of inflating the number of "yes" voters and forcing independent monitors out of polling stations.
"Flagrant forgery was the main headline of the last hours of this referendum," the organisation said in a statement.
Al Jazeera reporters were outside polling stations all day and saw few people voting, and Reuters described the turnout as a "trickle".
All major opposition groups including the Muslim Brotherhood, which won one-fifth of the seats in parliament standing as independents in 2005 elections, told their supporters to boycott the referendum.
Mohamed Habib, the deputy leader of the Muslim Brotherhood, said the government had made up the results.
"It is 100 per cent forged... They are lying," he told Reuters news agency.
Ayman Mohyeldin, an Al Jazeera correspondent, said he spoke to voters who did not understand why they were voting.
Mohyeldin also found people who voted though they were ineligible to vote.
He said government employees were taken en masse by buses to polling stations.
Amal Oweid, an Egyptian Mohyeldin spoke with, said: "I am here to vote for Hosni Mubarak... I am here to vote for him as president."
|Human rights groups estimate that less than|
10 per cent of the electorate voted [EPA]
She did not know how to read or write and did not know what was on the ballot.
Oweid said: "A guy came with me and he said "mark here" and I marked on the green circle ... I didn't know what the ballot said."
Mohyeldin reported that he was able to cast a ballot without providing appropriate Egyptian identification.
He said: "I came to the polling station [and] presented a press ID issued by the ministry of information that clearly stated that I am an American citizen working for Al Jazeera.
"I was handed a ballot and allowed to vote. At no time did I mislead authorities about my nationality or my identity."
There is no guarantee that the ballot will be tallied but the incident highlights major loopholes in the voting system, Mohyeldin said.