CAIRO — Egypt erupted into violent chaos Friday, raising doubts about the new authorities’ capacity to maintain order, as Islamists and other opponents of last month’s military takeover fought security forces and their civilian allies in street battles across the capital and other cities.

The country seemed to descend into anarchy. Terrified protesters caught in a cross-fire jumped or fell from an overpass in a panicked effort to escape. A gunfight erupted on the doorstep of a Four Seasons hotel. Men wielding guns and machetes — some backing the Islamists, others police supporters in civilian clothes, others simply criminals — roamed the streets of the capital and other cities, and it was often impossible to tell friend from foe.

Health Ministry officials put the civilian death toll for Friday at 27, but some news reports put it at more than 100, which would bring the death toll since Wednesday to nearly 750. In late afternoon more than 30 uncounted corpses were seen at a field hospital in a mosque near the center of the fighting, in Cairo’s Ramses Square. Defying a 7 p.m. curfew, antagonists battled there into the night, lit by an unchecked fire that consumed a nearby office building.

The military-appointed government issued a statement declaring that the military, the police and the people were “standing together in the face of the treacherous terrorist scheme against Egypt of the Brotherhood organization.” But the extent of the mayhem cast doubt on its ability to deliver on its central promise of restoring order and security.

Just two days ago, the police had routed thousands of protesters from sit-ins in support of the ousted president, Mohammed Morsi of the Muslim Brotherhood, killing several hundred.

The government suspended legal protections against arbitrary police action and authorized security forces to kill anyone who threatened a public facility.