The worst problem foreign election observers found on Sunday was the crowds, with some voters waiting hours to cast their ballots.
But the main opposition leader, Hailu Shawel, called for his coalition to reject the results even before polls closed, saying there had been massive irregularities that made it impossible for the vote to be free and fair.
Hailu said the four parties that make up his Coalition for Unity and Democracy would meet later on Sunday to make a final decision on whether to accept the results.
Prime Minister Meles Zenawi, known as one of the continent's more progressive leaders, has pledged his sometimes authoritarian government would introduce greater democracy.
Many have pointed to Sunday's race between the ruling coalition that ended a brutal dictatorship in 1991 and new opposition parties that promise greater liberalisation as a test of Meles's commitment to reform.
Provisional results are to be announced at each polling station on Monday, and official results will be certified on 8 June.
National Electoral Board Chairman Kemal Bedri said that by calling results into question, Hailu "is not doing justice to those people who have been standing in queues to vote for 10 to 12 hours. He has to be more responsible than that."
"It is a bit difficult to understand why those who are also responsible for the success, want to discredit it so early"
Top EU observer
Hailu made his call hours before the 6pm poll closing time.
Voters had overwhelmed the polls, and anyone in line at closing was allowed to vote.
More than 25 million people had registered and election officials estimated turnout at more than 85%, much higher than in 2000 elections that were seen as less democratic.
Ana Gomes, the top EU observer, was critical of the opposition call for results to be rejected. "It is a bit difficult to understand why those who are also responsible for the success want to discredit it so early," she said.
Meles had told reporters earlier that his government would accept defeat if international observers said the opposition had won.
"I was very proud and fought to make sure the Ethiopian people have the right to make their own decisions. I am now exercising it as an Ethiopian, and I'm very proud of this achievement," said Meles, a veteran of the rebellion that overthrew the dictatorship.
Meles told journalists that people should await the reports of foreign observers - monitoring the elections for the first time in Ethiopia's history - before making any conclusions on allegations of electoral abuses.
Prime Minister Meles Zenawi said
he was proud of the election
Gomes had told journalists that there has been some scattered irregularities and violence but that generally her observers told her voting went well and peacefully, but very slowly.
More than 500 foreign observers, including former US president Jimmy Carter and 24 teams from his human rights and development center, were monitoring the polls.
Voters began lining up before dawn. At day's end, some stations closed on time, but voters were still patiently waiting in lines at others. One election official said he expected his station to remain open until midnight to accommodate all voters.
"This is a chance to get democracy and elect someone who meets our needs," said statistician Firew Behu, who had been at his Addis Ababa station for seven hours and was told at 6pm to expect to wait another two hours to vote.
"If you are determined to do something, you have to insist on it"
"If you are determined to do something, you have to insist on it," Behu said, declining to say which party he supported.
Derje Woubeshet, an unemployed 29-year-old, said he was voting for the opposition Coalition for Unity and Democracy because he thought the ruling party had failed to create jobs.
But Wahib Toure, a cotton producer, said that complaints do not make a political agenda and that he would vote for the ruling Ethiopian People's Revolutionary Democratic Front.
Ethiopia was an absolute monarchy under Emperor Haile Selassie until the mid-1970s, when a brutal Marxist junta overthrew him.
Civil wars wracked the ethnically fractured country in the 1980s, and famine took as many as one million lives.
As many as a million lives were
lost due to famine
Meles' rebel group overthrew the junta in 1991. Meles became president, then prime minister in 1995, and is now seeking a third term.
In the 2000 vote, the ruling coalition took 534 of 547 seats in the lower house of parliament.
The country is divided into nine states along ethnic and linguistic lines, and each state has equal representation in the upper house of parliament.