Chadians were voting on Sunday in a presidential election as the incumbent, Idriss Deby, sought a fifth term in office.
President Deby, who took power in a military coup 26 years ago, faces 12 challengers but is widely expected to win another term.
In recent weeks, protest marches have been banned and government opponents imprisoned.
The opposition, which is fractured, boycotted the last election in 2011.
On Thursday, police fired live rounds and tear gas to disperse a couple of hundred protesters after prosecutors demanded six-month jail terms for five anti-government activist leaders.
On the campaign trail, Deby, 63, has hammered home a vow to promote the “emergence” of Chad, where seven out of 10 people cannot read or write, and half the population of 13 million live below the poverty line despite new oil revenues.
Oil production started in 2003 and now accounts for 60 percent of export earnings. But Chad ranks fourth from last in the UN Human Development Index, and more than one child in 10 dies before the age of five, according to World Bank estimates.
Chad also faces significant security threats with two attacks in the capital last year.
Deby has tightened security to address those threats while maintaining a strong presence in a regional force fighting the Nigeria-based Boko Haram group.
Some six million Chadians are eligible to vote on Sunday. Polling stations open at 0600 GMT.
Official provisional results may not be released until two weeks after voting day.