CNN reported the casualties occurred when security forces fired live rounds and tear gas during a large demonstration in Sanaa. Dozens of security personnel were seen in the vicinity of the attack.
Witnesses said the death toll is expected to rise because some of the wounds were severe, the news network said. An unnamed medic said at least 96 people were in critical condition.
"Central security forces brutally attacked tens of thousands of protesters who walked" from Change Square outside Sanaa University to call for the ouster of President Ali Abdullah Saleh's regime, Ali Kuraimi, a protester at the scene, told CNN.
Yemen Online reported hundreds of opposition protesters from the Islamic Islah party stormed the main university in Sanaa on Saturday, preventing classes from being held. They broke windows and tore down posters of Saleh.
Other dozens of schools across Yemen were closed as they were used as outposts by government forces and as shelters for people displaced by the ongoing turmoil, the news Web site said.
The New York Times reported at least eight explosions occurred in the capital early Saturday as militants fought Saleh's forces, plunging the city into darkness as electricity was knocked out. Protesters said the government forces employed some heavy artillery.
Doctors said eight protesters were wounded, the U.S. newspaper said.