Polling stations opened at 6 am (0400 GMT in the east; 0500 GMT in the west) and will close at 5 pm local time.
AFP journalists saw the first voter casting his ballot at a polling station in the eastern city of Kisangani, which sits in a region an hour ahead of the west of the huge country, which straddles two time zones.
Voting then began in several other cities, according to AFP teams, but with delays and bureaucratic difficulties.
One 30-year-old man, who had waited in line for three hours in the eastern city of Goma, said he was getting impatient and would soon give up. "We're tired. It's always a mess here," he said.
Logistical problems have plagued the organisation of this election, with the electoral commission struggling to transport voting materials to tens of thousands of polling booths on time.
Polls began to open at 9 am in Kinshasa, an AFP reporter saw, after long delays in setting up.
"I came here at 5 in the morning, I'm tired," said Germaine Kikongo, a 67-year-old civil servant, interviewed at a polling booth in the Kinshasa district of Lingwala at 8 am.
Voters still waiting in line at 5 pm will be given tokens and polling booths will stay open until they cast their votes, an official at the electoral commission told AFP.
The government declared a bank holiday for Wednesday, and as during previous elections, it closed the borders and suspended domestic flights.
Around 44 million Congolese, in a nation of 100 million, are registered to choose their president as well as lawmakers in national and provincial assemblies, and local councillors.
More than 100,000 candidates are running for various positions, and while counting is set to begin as soon as polling stations close, results are not expected to be announced for several days.
Several observation missions will be watching the voting process, with the largest one run by a union of Catholic and Protestant churches mobilising 25,000 election observers.
Leaders of this influential mission promised Tuesday to conduct a "parallel count" for the presidential election.
'Foreign candidates'
Tshisekedi, 60, faces 18 challengers.
The incumbent, who took office in 2019 and is running for a second five-year term, is considered the front-runner to win in the single-round presidential vote.
Tshisekedi's record, as he himself has acknowledged, is mixed. He has presided over years of economic growth but little job creation and soaring inflation. He is asking for another term to "consolidate his gains".
Throughout the campaign, he also poured scorn on what he termed "foreign candidates" -- suggesting that his opponents have dual loyalties and lack the will to stand up to Rwanda, which the DRC accuses of funding rebel groups on its soil.
Moise Katumbi, a 58-year-old businessman and former governor of mineral-rich Katanga province, is the main target of such attacks.
Armed conflict in eastern DRC overshadowed much of the electoral campaign. Militias have plagued the troubled region for decades, a legacy of regional wars that flared in the 1990s and 2000s.
Tensions have resumed since the M23 group, which is allegedly backed by Rwanda, began capturing swathes of territory in late 2021.
Clashes with M23 fighters have subsided in recent weeks but the rebels continue to hold sway over large parts of North Kivu province. Citizens living in those areas will not be able to vote.
Other presidential candidates include Martin Fayulu, a 67-year-old former oil executive who says he was the true winner of the 2018 election that brought Tshisekedi to power.
Surgical gynaecologist Denis Mukwege, 68, who won the 2018 Nobel Peace Prize for his work helping rape victims, is also running.
All the major opposition candidates say they suspect the government of preparing electoral fraud.
Flory Tshimanga, a 32-year-old seller of mobile phone credits in Kinshasa, said he thought the vote would proceed without hiccups.
"It's when the results come in that there could be problems," he said.
