Ethiopia's two main opposition groups say they are heading for victory in Sunday's poll, contradicting claims of victory from the ruling party.
Voter turnout was much higher than expected
The opposition CUD and UEDF groupings claim to have already won more than 200 seats in the 547-member parliament.
The ruling party says it has won more than 300 seats, but admit to losing all 23 seats in the capital.
The EU's chief election observer has criticised the parties for announcing results before counting is over.
"The EU election observation mission thinks that these announcements are not proper and will continue to follow the counting and tabulation closely," said Ana Gomes on Tuesday.
The election commission is not expected to give any provisional results before Saturday. Final results are not due until 8 June.
"The trend so far clearly indicates that the CUD will emerge as the winner with sufficient seats to form a government," Berhanu Nega, vice-chairman of the CUD, told a joint news conference alongside UEDF leaders.
He also alleged that the ruling party were seeking to tamper with results by asking for recounts in constituencies the opposition had won.
Information Minister Bereket Simon told the BBC that judging from poll returns the opposition had won about a third of seats.
The big opposition gains appear to have been made by the CUD - which draws its support from the Amhara community who have traditionally ruled Ethiopia.
They are demanding changes to the constitution and a tougher line with Eritrea - the country's northern neighbour, with which Ethiopia fought a bitter war over their disputed border.
There was huge 90% turnout reported in Ethiopia's third multi-party polls which were hailed by former US President Jimmy Carter as a "dramatic improvement" on previous parliamentary elections.
The BBC's Mohammed Adow in Addis Ababa says the opposition victory in the capital - and the defeat of the mayor - were not unexpected.
He says residents of the capital are the most politically active in the country, while the city is home to many unemployed people.
In rural areas, however, the government is everything - landlord, fertiliser, loans for farm tools and food aid during times of drought.
Opposition parties had only 12 seats before the poll, but set a target of jointly winning 185.
The European Union noted scattered irregularities, such as intimidation and children voting.
More than 300 foreign observers were allowed to check the vote, regarded as a crucial test of the country's fledgling democracy.
Twenty-six million Ethiopians were registered to vote at 30,000 polling stations.
Following opposition allegations of fraud, Prime Minister Meles Zenawi ordered a month-long ban on demonstrations.
Mr Zenawi also took control of the security forces in the capital Addis Ababa, in moves he said were meant to ensure post-election stability.