Greek Prime Minister Kyriakos Mitsotakis has called for the "swift resolution" of a probe into a crime journalist's shock murder, condemned by leading EU officials, political parties and unions.

"On (the PM's) express orders, the investigation will be expedited to the maximum degree," Citizen's Protection Minister Michalis Chrysohoidis told reporters after being summoned to an emergency meeting by Mr Mitsotakis.

Giorgos Karaivaz, who worked for private TV station Star and ran the news blog, was shot several times yesterday as he got out of his car outside his house in the southern Athens district of Alimos, witnesses said.

He had just returned home from work.

A police source said the 52-year-old journalist had been shot by two men on a motorbike. Seventeen bullet casings were recovered from the scene.

The police minister called the murder "a heinous crime", adding that "the victim's status as a journalist gives the case particular importance".

The murder was rapidly condemned by the European Commission and the Council of Europe commissioner for human rights.

"Murdering a journalist is a despicable, cowardly act," Commission chief Ursula von der Leyen tweeted yesterday.

"Europe stands for freedom. And freedom of press may be the most sacred of all. Journalists must be able to work safely," she said.

Mr Karaivaz had worked for some of Greece's leading newspapers and TV channels in a 32-year career.

"(He) was one of the most experienced crime reporters in the field... and was held in high regard by colleagues," the Esiea union of Athens daily newspaper journalists said in a statement.

The federation of Greek police officers said Mr Karaivaz was personally interested in improving working conditions for law enforcement and was "strongly critical of anybody" standing in their union's way.

While Greek media offices are frequently targeted in firebomb and vandalism attacks, journalist killings are rare.