Egypt's Islamist presidential candidate Mohammed Mursi sought on Tuesday to reassure Coptic Christians and women, who fear a conservative Islamist in power could threaten their freedoms.

"Our Christian brothers, let's be clear, are national partners and have full rights like Muslims," Mursi told a press conference, as political upheaval and violence plague the country ahead of a runoff.

Copts "will participate in a presidential institution" said Mursi, who is to face Ahmed Shafiq, the last premier of deposed president Hosni Mubarak, on June 16-17.

The Muslim Brotherhood is opposed to a woman or a Christian being president, but the movement's political arm the Freedom and Justice Party says it is not.

Egypt's Christians, who make up about 10 percent of the 82 million population, complain of discrimination and have repeatedly been the target of attacks.

Mursi also promised to "respect women's right to work in all areas, to choose the way they dress", saying there would be "no imposition on women to wear the veil."

He insisted that the Islamist movement, which already dominates parliament, was not seeking to "dominate" the country, vowing that a new constitution would "satisfy everyone."

Mursi was speaking hours after the Shafiq's campaign headquarters were torched by angry protesters hours after the electoral commission announced Shafiq would face Mursi in the runoff.

Media said Prime Minister Kamal al-Ganzuri would meeting with ministers and governors in the wake of the attack, after a senior military official said the army had plans to deal with any violence ahead of the decisive election.

Police, who were on alert, said eight suspects were arrested near the office following the attack.

The protesters ransacked Shafiq's office, according to a correspondent who visited the building in the middle-class Dokki neighbourhood of Cairo on Tuesday.

They had broken or toppled every piece of furniture inside the two-storey villa late on Monday, and also set alight an annex of the headquarters.

Several doors, windows and mirrors inside the office were broken, while the street outside the villa was littered with campaign leaflets that cleaners were busy collecting.

"The premises will be refurbished and Mr Shafiq will continue to use them to lead his campaign," said Ahmed Abdel Ghani, a Shafiq supporter.

After the attack, some of the protesters returned to Cairo's iconic Tahrir Square, throwing Shafiq's campaign leaflets in the street.

Many appeared to be supporters of an unsuccessful left-wing candidate and opposed both Shafiq and Mursi.

There were no immediate reports of injuries at the headquarters and fire fighters said the blaze was quickly put under control.

"We were inside when they attacked us," one member of Shafiq's campaign staff said. "They set fire to the garage that had general Shafiq's campaign literature."

Earlier around 1,000 protesters had gathered in Tahrir Square to protest Shafiq's presence on the runoff ballot.

Announcing the results, electoral commission Chief Faruq Sultan had said no candidate won a majority in the first-round vote on May 23-24, so the two with the highest votes, Mursi and Shafiq, would face each other in a runoff.

Mursi won 24.77 percent of the votes in the first round, slightly ahead of Shafiq's 23.66 percent.

Leftist candidate Hamdeen Sabbahi came third with 20.71 percent, ahead of moderate Islamist Abdel Moneim Abul Fotouh with 17.47 percent.

Former foreign minister Amr Mussa was fifth, trailing with 11.12 percent.

The commission put the official turnout in the vote -- the first since the 2011 uprising that ousted Mubarak -- at 46 percent of the 50 million people eligible to cast ballots.

Both Mursi and Shafiq, who represent polar opposites in the country's fragmented politics after last year's uprising, are now trying to court the support of the losing candidates and their voters.

The Brotherhood, which alienated many other political parties after its domination of parliamentary elections last winter, has warned Egypt would be in danger if Shafiq wins and has pledged to become more inclusive.

Two of the losers, Mussa and Abul Fotouh, declined to endorse either of the front runners.

The contest presents a difficult choice for activists who led the revolt. For them, choosing Shafiq would be to admit the revolution had failed, but a vote for Mursi could threaten the very freedoms they fought for.

The election has followed a tumultuous military-led transition from autocratic rule that has been marked by political upheaval and bloodshed. But it also witnessed free parliamentary elections, which saw the two main Islamist parties clinch nearly three quarters of the 498 seats in the legislature.

The Supreme Council of the Armed Forces, in power since Mubarak's downfall, has pledged to restore Egypt to civilian rule by the end of June.