Sporadic gunshots continued for about two hours in Tahrir Square in downtown Cairo early Thursday and casualties were reported, the Al-Jazeera TV channel said.
Cracks of gunfire were clearly heard in the square, where large crowds of protestors still gathered to press ahead with their demand for President Hosni Mubarak's resignation, live video footage showed, Xinhua reported.
Unconfirmed reports said at least five people were killed and 15 others wounded from bullets, citing doctors at the scene.
There is no way to confirm who fired the shots. Clashes between supporters of Mubarak and anti-government protestors have killed at least three people and wounded some 600 hundred on Wednesday.
Al-Jazeera reports said military tanks were redeployed among protestors following the shooting. Video footage showed that Molotov cocktails and stones were hurled toward protestors in the square.
Protests turned violent in the last few hours after a week of peaceful vigil in the square. Kicking, beating, shoving, burning, and verbal fights started as pro- and anti-Mubarak protesters encountered in Tahrir Square, epicenter of the demonstration.
Though some of Mubarak's supporters pledged to "liberate Tahrir square with blood," the overall situation was largely under control. Many ordinary people did not want violence at all.
Mubarak, 82, announced Tuesday that he would not seek re-election for the post he has held since 1981, but protesters said they wanted the president to step down before Friday and planned a massive protest on the day.
UN Secretary General Ban Ki-moon expressed his great concern Wednesday at the "unacceptable" violence in Egypt.
"I am deeply concerned by the continuing violence in Egypt," Ban said, urging all parties in Egypt to engage into a dialogue without any delay.
But newly appointed Egyptian Vice President Omar Suleiman insisted that there would be no dialogue between the government and the opposition until the protests stop.
After more than a week of nationwide protests, Egypt has been plunged into chaos as many worry that the protests would bring the country into long-term political turmoil.
The United States has clarified its stance over the chaos in Egypt as President Barack Obama said the orderly transition in Egypt "must begin now."
Obama said on Tuesday that he spoke directly to Mubarak and the Egyptian president recognized that "the status quo is not sustainable and that a change must take place."
"What is clear, and what I indicated tonight to President Mubarak is my belief that an orderly transition must be meaningful, it must be peaceful, and it must begin now," Obama said.