Rare protests against President Abdel Fattah el-Sisi erupted in central Cairo and several smaller Egyptian cities on Friday night as hundreds of young people, responding to online calls for demonstrations against government corruption, chanted “Down with Sisi” and “Leave now.”

The protests, although small, occurred as Mr. el-Sisi flew to New York to attend the United Nations General Assembly next week — and they were unusual for taking place at all.

Mr. el-Sisi, who came to power in a 2013 military takeover, has cemented his hold through harsh repression that has silenced critics, curtailed free speech and ended any semblance of democratic politics. Even the mildest dissent has been met with harsh punishments and long prison sentences.

On Friday, the police fired tear gas to disperse some groups, but other protesters continued to clash with the police into the early hours of Saturday.