Doctors at Greek state hospitals and public health centres have walked out on strike to protest against planned spending cuts.
Medics, who claim healthcare reforms will lead to worse services for patients, staged a sit-in at the health ministry.
Athens, meanwhile, was left without most forms of public transport as striking unions protested against the planned restructuring of their loss-making state-run companies.
Transport unions have held a string of strikes over the past two months against planned pay cuts and involuntary staff transfers that are expected to be approved in parliament this month.
Greece is locked in a harsh austerity programme after narrowly avoiding bankruptcy last year.