Protesters in Greece briefly clashed with riot police Wednesday amid a general strike and demonstrations over price hikes and spiralling inflation.

Hooded youths in Athens and Thessaloniki threw firebombs at police, who fired back with tear gas, an AFP photographer said.

Firebombs were also thrown at a car in front of the Finance Ministry in Athens and red paint was splashed at the entrance of the Greek central bank's headquarters.

Eight people were held for questioning in Thessaloniki after the protest, local police said.

Some 20,000 protesters had earlier marched in the capital, double the number of people who participated in the last general strike in April, police said.

Another 8,000 people demonstrated in Thessaloniki, the authorities said.

"We choose life, not survival," read a banner in the northern Greek port city.

Athens' normally busy roads were all but empty, with the walkout affecting bus, underground, tram and suburban train services as well as taxis.

Boat services from the mainland to the Ionian Islands and those in the Aegean Sea were also halted by the industrial action.

Energy-linked price hikes, largely fuelled by the ongoing war in Ukraine and sanctions on Russia, have sent inflation to its highest rate in three decades in Greece.

"The cost of living is untenable," read a large poster for the country's biggest union, the GSEE, also calling for salary increases and "social protection for all".

Prime Minister Kyriakos Mitsotakis' government has announced a 5.5-billion-euro package of aid which includes a 250-euro subsidy to 2.3 million vulnerable citizens in December and an increase in the student housing allowance.

But unions insist on the need for salary rises, not hand-outs, amid double-digit inflation in the last six months which rose to 12 percent in September.