Abiy, who has ruled the Horn of Africa nation of 130 million people since 2018, is criticised for growing authoritarianism, in contrast to his early years when he won the Nobel Peace Prize for mending relations with neighbouring Eritrea.

Despite internal conflicts, repression and high poverty rates, Ethiopia's economy is seeing fast growth thanks largely to a state-led construction boom and surging exports such as coffee.

"The coming five years will be a period of historic transformation for our nation," Abiy told reporters after casting his ballot in his native Oromia region, home to the largest of Ethiopia's 80-odd ethnic groups.

"Achieving this change will demand even greater determination, sacrifice and effort than we have demonstrated in the past," he said.

Long queues formed at polling stations in the capital Addis Ababa, AFP journalists saw, with some waiting since 2:00 am.

Later, the authorities unexpectedly extended voting by six hours, saying they would stay open to midnight.

"It is a critical time to decide the fate of our country," said Binyam Gideyelem, 38, a telecoms worker voting for the first time, at a station near the international airport.

Despite the enthusiasm -- in a country where the population is under close surveillance -- analysts say the vote is little more than a formality to keep Abiy in power.

Abiy's PP won 96 percent of the seats in the last parliamentary election in 2021 and is running unopposed in dozens of the 547 constituencies this time.

Independent journalists are stifled, opposition parties divided and under-resourced, and the country faces multiple insurgencies that make monitoring in conflict areas all but impossible.

The head of the election board, Melatwork Hailu, told reporters that 143 of roughly 48,000 polling stations were not opened due to "security issues" and said voting was "interrupted" in others, without giving details.

The election is "likely to be among the least competitive of the seven national elections held since multiparty democracy was introduced in 1991," Ahmed Soliman and Abel Abate Demissie of the Chatham House think tank wrote last week.

"Many challengers to the ruling PP will not contest the elections," they noted. "Some are in exile, some are banned, some are imprisoned, and many may see little incentive to abandon their armed struggle against the government."

Results are expected by June 11.

- Rapid growth -

No election is taking place in the northern region of Tigray, due to ongoing tensions between regional and federal authorities.

More than a million people remain displaced from its brutal civil war of 2020-2022.

Ethiopia also faces insurgencies in the two most populous states, Oromia and Amhara.

In Amhara, with a population around 20 million, Fano nationalist militias have threatened to disrupt the electoral process, while a group called the Oromia Liberation Army is also active against federal forces.

Ethiopia also has tense relations with neighbours.

Abiy has angered Somalia and Eritrea with his push to gain direct sea access for the landlocked country, Egypt fears the impact of a new megadam on the Nile, and Sudan accuses him of backing Sudanese rebels.

Despite the challenges, the International Monetary Fund expects the economy in Africa's second most populous country to grow by more than nine percent this year -- one of the fastest rates in the world -- largely thanks to infrastructure and industrial investments under previous governments.

Abiy has made tentative steps to open up the economy, which has boosted exports, but Ethiopia still faces huge debt, high inflation and a poverty rate around 40 percent.

Observers from the African Union, headquartered in Addis Ababa, as well as the East African regional bloc IGAD, are monitoring Monday's poll.

Ethiopia did not accept a proposal from the European Union to send observers, according to an EU source.