A group of protesters stormed and torched the campaign headquarters of presidential candidate Ahmed Shafiq, as tensions continued to rise after the presidential election results were announced.
Protesters raided Shafiq's election HQ, looting and setting offices on fire.
Heba Hamed, a worker in the offices said all staff had been evacuated andf there were no injuries.
Police rounded up protesters shortly after the fire was set.
Local press said protesters were chanting anti-Shafiq slogans, accusing him of being a remnant of the Hosni Mubarak regime.
Shafiq was appointed prime minister by Mubarak, just before the dictator was forced to step down in February 2011 as the country rose up against him.
Shafiq's supporters gathered around his headquarters shortly after ther attack, chanting "Down with the Supreme Guide [of the Muslim Brotherhood]" and "The poll will show Shafiq is the president".
The assault by anti-Shafiq protesters came after it was announced that he would compete in a run-off against the Muslim Brotherhood's candidate Mohammed Morsi in June.
The announcement of the official results provoked the revolutionaries, with fresh protests reported in Cairo's Tahrir Square as well as Alexandria, Suez and Port Said.
In Cairo, thousands of protesters took to the streets and marched to the high court to protest against the two run-off candidates.
Demonstrators carried banners criticising the outcome of the elections, chanting slogans such as "No remnants of the former regime and no Brotherhood, the revolution is still at the square" and "Hosni Mubarak still rules".
They also denounced what they said was vote-rigging after appeals filed with the electoral commission alleging violations in the first round of the elections were rejected.
In Alexandria, hundreds of people also demonstrated. In Suez the April 6 movement and the Revolution's Youth movement also organised a march.