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 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.