Broadcasts of the huge protest rally were allowed, in a change from Thursday, The New York Times reported.
Al-Jazeera, a chief target of the Hosni Mubarak regime, said the Cairo office of its Arabic service had been stormed by "a gang of thugs."
"The office has been burned along with the equipment inside it," the network said Friday. "Al-Jazeera has also faced unprecedented levels of interference in its broadcast signal as well as persistent and repeated attempts to bring down its Web sites."
Al-Arabiya, whose reporters were chased from their office Thursday, reported that the army had been ordered Friday to protect foreign journalists, but scattered reports of attacks continued.
Amnesty International and Human Rights Watch demanded that authorities reveal the whereabouts of and release activists, lawyers and journalists arrested in a raid Thursday. They include staff from both groups.
Colleagues of the Egyptian lawyers arrested said the group is being held at an army base on the outskirts of Cairo, but when they went to see them, the army refused to confirm their detention.
Earlier, U.S. Secretary of State Hillary Clinton denounced attacks on journalists in Cairo.
"We condemn in the strongest terms attacks on reporters covering the ongoing situation in Egypt," Clinton said at the State Department. "This is a violation of international norms that guarantee freedom of the press and is unacceptable under any circumstances."