A giant lion roars against the backdrop of a battered Greek flag in wall art covering the side of a school building in a working-class Athens suburb.

The creation is one of many examples of street art across the Greek capital expressing the despair of ordinary people after four years of government belt-tightening at the behest of international creditors.

Greece's radical leftist party Syriza, which opposes the government's austerity policies, was leading in the key Athens area, exit polls from the first round of local elections showed on Sunday.

Syriza's candidates for the capital's mayor as well as regional governor in greater Athens were ahead in the race against the incumbent socialist office-holders, the televised polls showed.

An undersea earthquake measuring 4.8 on the Richter scale hit near the Greek island of Andros early Wednesday and was felt in the capital, the Athens Observatory said.

No damage or injuries were reported from the Aegean Sea tremor, which occurred 126 kilometres (78 miles) east of Athens at 0403 GMT.

A booby-trapped car exploded outside the Bank of Greece in central Athens Thursday but no one was injured in the blast, police said, as Greece was set to return to the debt markets after a four-year absence.

The car which was parked on the sidewalk facing the central bank building blew up around 0255 GMT. The building is close to the office of Greece's international lenders.

Several thousand protesters have joined a demonstration in central Athens after the Health Ministry ordered the closure of the country's entire state-run outpatient clinic network for one month to reorganize the health system.

The protest organized by a Communist labor union ended peacefully Tuesday outside the ministry.

Unknown attackers fired shots at the German ambassador's residence in northern Athens early on Monday but caused no injuries, police sources said.

The attack happened around 3:30 am (0130 GMT) and the assailants are thought to have fled by motorbike.

Work is finally set to begin on Athens' first mosque, 13 years after plans were first announced, the Greek government announced on Thursday.

A Greek consortium has been chosen, the infrastructure ministry said, after five previous attempts to find a business group to lead the project failed.

Police in Athens on Friday said they had arrested a Greek couple suspected of having purchased a Roma baby for 4,000 euros ($5,500).

The couple, a 53-year-old man and his 48-year-old wife, told police that they had received the baby girl, only a few weeks old, from a Roma woman in March.

Greek authorities have sought help from Interpol to identify a young blonde girl whose discovery in a Roma camp has sparked worldwide concern and interest in other child disappearance cases.

The cross-border police agency said it has sent out the girl's photo and DNA profile to all of its 190 member countries.

Aristotle, Plato and Socrates have resurfaced in Athens in the midst of Greece's harrowing economic crisis, brought to life by a global philosophy congress in the very locations they once frequented.

"It's very important to find oneself in the place where philosophy was born," said Ivorian professor Tanella Boni, one of over 2,000 philosophers from 105 countries who attended the seven-day event which wrapped this weekend.