Deadly fighting in the oil-rich Niger Delta marred the electoral race for weeks. Ethnic Ijaw militants in the volatile southern region appeared determined to carry out threats to block polling because of a dispute over voting districts.
There were scattered reports of election day violence and intimidation. Yet voting went ahead peacefully in many cities, where the biggest problem appeared to be a seasonal downpour that delayed arrival of voting materials for hours. As a result, many stations stayed open well after the official closing time of 3:00 p.m. local time.
Voting in some trouble areas was held over until Sunday, when results from other areas were expected to start coming in.
Although figures were unavailable, election commission chief Abel Guobadia said early returns indicated a high turnout across the country of 126 million people. Sixty-one million voters are registered for Saturday's ballot, which features 3,000 candidates.
The balloting for 469 seats in the House of Representatives and Senate was run by civilians. Military coups have scuttled Nigeria's previous attempts to hold democratic, civilian-run elections.
Saturday's ballot preceded presidential elections April 19 that will pit President Olusegun Obasanjo — a former military ruler turned civilian leader — against 19 opposition candidates, including three former army generals.
"If the problems seen today are not addressed … they could impact very negatively on the presidential elections," warned Festus Okoye, head of the private Transitional Monitoring Group, which provided 10,000 poll observers.
Party agents, in some cases, were accused Saturday of intimidating voters, who were often forced to cast their votes in full view of bystanders, Okoye said.
Some complained they had been unable to vote at all. Among the most prominent omissions were Aisha Buhari, wife of another presidential contender, former junta leader Muhammadu Buhari, who was told her name was not on the voter's list in Sarkin Yara, near the northern city of Daura.
Buhari's All Nigeria Peoples Party accused Obasanjo's Peoples Democratic Party of withholding election materials in a bid to prevent their opponents' supporters from voting.
"Defeat was staring them in the face," the opposition group said in a statement that accused their ruling party opponents of planning to inflate their own vote total and "declare results of elections that never took place."
On Saturday, witnesses said four people including two policemen were killed in an armed ambush on opposition politician Fidel Ayogu. In Lagos, the commercial capital, Associated Press journalists saw three men with stab wounds from what witnesses said was a brawl between ruling party and opposition supporters. There were also unconfirmed reports of violence in the eastern city of Port Harcourt.
In Ogbe-Ijoh, an Ijaw town 20 miles south of the oil port of Warri, police told an Associated Press reporter their station was attacked overnight by Ijaw youths who beat up several officers.
Election commission officials fled the town overnight and have not returned. There was no sign of voting.
Ijaw militants told The Associated Press they also blocked voting in dozens of other villages, although this could not be independently confirmed.
In Warri city, voting started six hours late and was extended until Sunday, electoral commission official Babayo Shehu said.
Ethnic Ijaws had pledged to prevent the elections in Ijaw-dominated parts of the swampy Niger Delta, where most of Nigeria's oil is drilled. The militants are angry authorities refused to change electoral boundaries, which they say favor rival Itsekiris.
Ijaw militant leader Dan Ekpebide warned late Saturday "it will be bloody" if officials tried to extend voting in their areas on Sunday.
The threat came after weeks of fighting between ethnic militants and government troops. The violence left more than 100 people dead and shut down 40 percent of the country's oil production. Nigeria is the fifth largest supplier of U.S. oil imports.
President Obasanjo, who voted during a heavy downpour near his home in Abeokuta, denied allegations of intimidation.
"I don't think that there is anyone who has genuinely registered who will not be allowed to vote," Obasanjo said.
The legislative elections are the first since 1999, when the former military regime administered the polling.
More than 10,000 people in Nigeria have been killed in political, ethnic and religious violence since Obasanjo was first elected in 1999, ending 15 years of brutal military rule.
By Glenn McKenzie