Egyptian naval conscripts help an elderly man into a polling station as others queue behind him to cast their votes in Egypt's second city of Alexandria on the first day of voting in the 2018 presidential election on March 26, 2018 (Photo: AFP)

Egyptians headed to the polls Monday in a presidential election to choose between incumbent Abdel Fattah al-Sisi and a little-known politician who has struggled to make the case he is a serious contender.

Polling stations opened at 9:00 am (0700 GMT) for the three-day vote, in which Sisi is all but guaranteed to win a second four-year term.

The president was among the first voters, shown on Egyptian television casting his ballot at a school in Cairo's Heliopolis district under tight security.

Voters turned up early at polling stations and queued to cast their votes. Outside some stations, musical troupes showed up to celebrate the election.

"What's the alternative other than Sisi? If we don't come to vote would that benefit the country?" said Adel Sameeh, 66, an insurance consultant.

Security forces were deployed across the country to protect polling booths and armoured vehicles were stationed at several points around Cairo.

"Nothing will scare the Egyptian people. Not terrorism or anything else," Prime Minister Sherif Ismail told state television after casting his vote.

The Islamic State group's Egyptian affiliate, which has killed hundreds of soldiers and civilians, has threatened attacks on election infrastructure.

On Saturday, two policemen were killed in a car bomb attack targeting the provincial head of security for the northern Alexandria governorate. The security chief was unharmed.

Some 60 million people in Egypt, the most populated Arab country, are registered to vote on March 26, 27, and 28. Official results are expected on April 2.

They will have the choice between Sisi and Moussa Mostafa Moussa, who registered immediately before the close date for applications, saving the election from being a one-horse race.

Moussa, who has denied he is a "puppet", had been leading a Sisi re-election campaign until he registered as a candidate.

"I call on everyone to participate strongly during these three days," he told reporters before casting his ballot.

Other opponents have been sidelined, including former military chief of staff Sami Anan, who was detained in January, shortly after announcing his candidacy.

The military said the reserve general broke the law by illegally declaring his candidacy.

In an interview broadcast on Egyptian television last week, 63-year-old Sisi said the lack of serious opponents was not his doing.

"I wish we had one, or two, or three, or 10 of the best people and you choose however you want," he said.

Sisi won his first term in 2014, a year after the former army chief ousted his predecessor Mohamed Morsi following mass protests demanding the divisive Islamist's resignation.

In that election, Sisi faced Hamdeen Sabbahi, an established left-wing politician much better known than Moussa. Sisi won with 96.9 percent of the vote.

With Sisi's victory effectively guaranteed, authorities will be hoping for a large turnout to enhance the vote's legitimacy.

The governor of the northern Behaira province, Nadia Abdo, told a television station that she said to district heads "tell people that the district with the most votes cast will have water, sewage and electricity."

Sisi has stressed in his pre-election appearances the importance of voters turning out in large numbers.

In 2014, about 37 percent of voters participated in the two-day election, prompting authorities to add a third day to obtain a final participation rate of 47.5 percent.

It is unlikely that this year's turnout will even reach the 37 percent threshold, said analyst Mostafa Kamel al-Sayed.

"The result is known in advance, and this does not encourage Egyptians to go out and vote," he said.

During the campaign, Sisi appeared frequently on television and in newspapers, hailing factories and infrastructure projects built over the past four years.

Egyptian cities, especially Cairo, are flooded with banners showing Sisi and messages of support from business owners. Posters vowing support for Moussa, 65, are rarely seen.

But with an economic crisis and gruelling price hikes -- and the return of a regime seen as at least as authoritative as that of ex-leader Hosni Mubarak -- support for Sisi appears to be slightly in decline.