N’DJAMENA, Chad — President Idriss Deby of Chad faced off against more than a dozen challengers Sunday as he seeks another term after more than 25 years in power in this central African nation which is battling Islamic extremists.

The election comes amid mounting international concern about Chad’s human rights record. Four activists are awaiting verdicts on charges of trying to disturb the peace and resisting arrest. Internet access was down in the capital of N’Djamena on election day, residents reported.

Deby, who has been in power since 1990, could face a second round of voting because of the large number of candidates. It could be one of the toughest challenges he has faced, according to Thibaud Lesueur, central African senior analyst for the International Crisis Group.

‘‘It’s quite unprecedented to have so many people in the street,’’ he said, noting that many have been afraid to demonstrate against the incumbent.

Chad, a former French colony, is now home to the French military’s operations in Africa.