Ethiopia's ruling party and its allies have won an overwhelming majority in parliament in weekend elections, the country's electoral board announced Wednesday.

The EPRDF, in power in Africa's second-most populous nation for over two decades, were widely expected to secure a near clean sweep of parliament, and the outgoing chamber had just one opposition MP.

According to preliminary results, the ruling Ethiopian People's Revolutionary Democratic Front (EPRDF) of Prime Minister Hailemariam Desalegn secured all 442 parliamentary seats so far declared out of the 547 seats up for grabs, said Merga Bekena, president of the National Electoral Board of Ethiopia.

Ahead of Sunday's polls, which African Union observers said passed off without incident, the opposition alleged the government had used authoritarian tactics to guarantee victory.

But government spokesman Shimeles Kemal celebrated the win as the result of Ethiopia's economic advances.

"Voters have credited the ruling party for the economic progress it introduced in the country," he told AFP.

"They want the continuation of this policy. In view of the weak, fragmented opposition and the lack of viable alternative, it was very likely that the ruling party would win in a landslide."

According to the electoral board, the EPRDF also took back the only seat that was held by the opposition, securing all 23 seats in the capital Addis Ababa.

Ethiopia, whose 1984 famine triggered a major global fundraising effort, has experienced near-double-digit economic growth and huge infrastructure investment -- making the country one of Africa's top-performing economies and a magnet for foreign investment.

It also remains a favourite of key international donors, despite concerns over human rights, as a bastion of stability in an otherwise troubled region.

- 'Imprisonment, intimidation, interference' -

According to the government spokesman, "voters have made stability, peace and security vital in their decision and for the past two decades the ruling party has secured stable and reliable security."

Ethiopia's former Marxist rebel-turned-leader Meles Zenawi, who died in 2012, was succeeded by Prime Minister Hailemariam, who has said he is committed to opening up the country's political system to allow more space for opposition parties.

But rights groups routinely accuse Ethiopia of clamping down on opposition supporters and journalists, and of using anti-terrorism laws to silence dissent and jail critics.

Activists have said the polls would not be free or fair due to a lack of freedom of speech.

The United States, which enjoys close security cooperation with Ethiopia, also said it remained "deeply concerned by continued restrictions on civil society, media, opposition parties, and independent voices and views."

"The imprisonment and intimidation of journalists, restrictions on NGO activities, interference with peaceful opposition party activities, and government actions to restrict political space in the lead-up to election day are inconsistent with these democratic processes and norms," the State Department said in a statement.

A statement from the European Union also said true democracy had yet to take root in Ethiopia.

"Arrests of journalists and opposition politicians, closure of a number of media outlets and obstacles faced by the opposition in conducting its campaign have limited the space for open debate and had a negative impact on the overall electoral environment," the EU said.

The African Union had deployed 59 observers for Sunday's polls, but European Union and Carter Center observers, who were present for the 2010 vote, were not invited.

On Tuesday the AU observer mission said the elections were "credible" and "generally consistent with the AU guidelines on the conduct of elections in Africa."