Robert Abela is set to become the new prime minister of Malta after incumbent Joseph Muscat's downfall over the murder of an investigative journalist.

Abela, who is seen as representing continuity, was elected leader of the Labour Party, meaning he will automatically take on the role of prime minister on Sunday.

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Muscat, 45, announced in December he would quit following widespread anger over his perceived efforts to protect friends and allies from a probe into the 2017 killing of investigative journalist Daphne Caruana Galizia. He is set to resign later on Sunday.

In the run-up to the election, Abela refrained from criticising Muscat.

Before the election result, activist groups cast doubt on whether Muscat's successor would bring about real change in the country, which they say has been taken over by "criminals".

Dubbed the "one-woman WikiLeaks", Caruana Galizia exposed corruption at the highest levels. She was killed by a car bomb on October 16, 2017, in an attack that made world headlines.

Less than an hour before her death, she wrote on her blog: "There are crooks everywhere you look. The situation is desperate."

Some 17,500 Labour voters were expected to vote for the party's first mid-term prime minister in history.

Investigative journalist Caruana Galizia was killed after her car exploded outside her home in October 2017 [File: Rene Rossignaud/AP Photo]

Two candidates were vying to take over as Labour leader and prime minister: Deputy Prime Minister and Minister of Health Chris Fearne, a 56-year old surgeon, and 42-year-old lawyer Abela.

Fearne had the backing of most cabinet members but Abela had been closing the gap in the polls in the final week of the campaign, the Times of Malta said.

'We need change'

Neither referred to the Galizia killing in the run-up to the election. Both have insisted they represent continuity, highlighting their determination to keep the economy on its stellar trajectory.

"We have the reputation (in Malta) of being pirates. The reason is that a group of criminals have taken over our government," Manuel Delia, a member of the activist group Repubblika, told AFP.

"We need change."

Martina Darmanin, a 24-year old academic, said the reporter's killing had been "a shock", and she had taken part in the regular demonstrations denouncing "the mafia in power".

"As a member of the EU we want and we deserve better than this: good governance, rule of law," she said, adding that she was "fed up of hearing that I'm from a tax haven country".

Protests demanded justice for the murder of journalist Caruana Galizia [File: Darrin Zammit Lupi/Reuters]

Repubblika plans to deliver a manifesto to the new prime minister calling for a clean up of politics and the economy, as well as a revamp of the constitution to guarantee a genuine separation of powers.

In an emotional farewell address on Friday, Muscat said he was "sorry" about the killing, the investigation into which he has been accused of hampering.

"I paid the highest price for this case to be solved under my watch," he said.

The opposition Nationalist Party sharply criticised Muscat's "surreal" speech, pointing out that it was Caruana Galiza who had paid that price.

'An indelible stain'

Muscat's fall from power followed daily protests led by supporters of the Caruana Galizia family, who accuse him - among other things - of shielding his chief of staff and childhood friend Keith Schembri, who has been implicated in the murder.

The journalist's family had called for Muscat to step down immediately, but support from his party and his own popularity - linked to Malta's booming economy - bought him time until the party election.

Three men are on trial for allegedly detonating the bomb that killed Caruana Galizia, while a fourth - powerful businessman Jorgen Fenech - was charged as an accomplice after being detained as he tried to leave the country on his yacht.

Fenech's arrest in November sparked the resignation of Minister of Tourism Konrad Mizzi, who formerly served as energy minister, and Schembri.

The murder and probe, Malta Today wrote on Saturday, "cast an indelible stain on Muscat and his administration".