"There are riots, police are cracking down ... heard shooting. There are some injured," the photographer said.
Television images showed demonstrators throwing rocks at police, who responded with a wave of tear gas.
Zelaya was ousted from power by the Honduran military on Sunday and whisked away to Costa Rica, sparking international outcry and calls for him to be returned to power.
But within hours Congress had appointed its speaker Roberto Micheletti as interim president until the current presidential term ends in January.