CAIRO — Egyptians cast their ballots Saturday on the first of three days of voting on constitutional amendments that would allow President Abdel-Fattah el-Sissi to stay in power until 2030 and broaden the military’s role.

Critics have blasted the proposed changes as another major step toward an authoritarian government perhaps even more severe than that of former President Hosni Mubarak, whose nearly three decades of autocratic rule was ended by a popular uprising in 2011.