Ethiopia's main opposition coalition has accused the ruling party of trying to cling to power by announcing premature results from Sunday's poll.
The capital's residents are more politically active than elsewhere
The ruling EPRDF has claimed it has won by a large majority, although official results have not yet been declared.
The opposition CUD has meanwhile claimed victory in the capital, Addis Ababa, with several ministers losing their seats in parliament.
There was a massive turnout in Ethiopia's third multi-party polls.
The chief European Union election observer has also criticised the ruling party for announcing results before counting is over.
"This is improper and it is particularly improper from the ruling party to do it at this stage. We are now at a very important and critical stage, which is the issuance of the results," said Ana Gomes.
"This is a clear sign that the ruling party wants to cling to power using all illegal means that will suppress the democratic will of the people," said CUD (Coalition for Unity and Democracy) vice-chairman Berhanu Nega.
Information Minister and EPRDF (Ethiopian People's Revolutionary Democratic Front) spokesman Bereket Simon told the AP news agency that the ruling party had won at least 300 seats in the 547-member parliament.
"This is a very positive result for us," he said.
He said the opposition victory in the capital showed how democratic the election had been.
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.
Results from the country's vast rural areas were expected to turn the tally in favour of the ruling EPRDF.
The ruling party say they have won regional assemblies in four states: South Ethiopia Peoples, Oromia, Amhara and Tigray.
Opposition parties had only 12 seats before the poll, but set a target of jointly winning 185.
Provisional results are expected at the weekend, with final results on 8 June.
Mr Meles' party is widely tipped to win
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.
The main opposition party, the Coalition for Unity and Democracy (CUD) complained of alleged election fraud and mass arrests of their election observers but pulled back from calls to reject the entire results.
But former US President Jimmy Carter said it was a "dramatic improvement" on previous parliamentary elections.
The European Union noted scattered irregularities, such as intimidation and children voting but said it was too early to reject the results entirely.
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.