Police in Athens fired tear gas at stone-throwing protestors Wednesday as thousands of Greeks walked off the job to join the debt-ridden country\'s first general strike this year and oppose austerity measures. About 15,000 striking workers took part in a Communist-organised demonstration in Athens and 20,000 more joined protests organised by other unions, according to police figures. Another 15,000 people marched in Greece\'s northern metropolis Thessaloniki, local authorities said. Protesters tried to firebomb a car in Athens and threw rocks at police, who fired back tear gas, while in the city of Iraklio on the island of Crete, demonstrators overturned a squad car, police said. \"Unpaid bills, slashed wages and pensions, boarded-up shops. Greek people cannot wait for saviours. Only by taking their fortunes into their own hands can they exit the stalemate,\" main opposition leader Alexis Tsipras, head of the radical leftist Syriza party, told reporters. The nationwide strike -- the first general work stoppage in Greece this year -- forced airport authorities to scrap or reschedule dozens of flights while hospitals operated on reduced staffing. Ships were to remain docked throughout the day, disrupting ferry services to the islands. And although most public transport was to run, buses and train services expected disruptions. Doctors, lawyers and teachers took part in the protest action organised by private sector union GSEE and the public sector ADEDY. \"No to modern sweat-shops, hands off collective labour agreements,\" read the main banner carried by Communist demonstrators in Athens. \"Everybody I know is unemployed,\" said Alexandra Papadatou, a 28-year-old jobless economist. \"I am fighting on the streets for this government, which passes all these measures, to fall,\" she told AFP. \"I am considered lucky because at least I have a salary, about 600 euros,\" said Panayiotis Kolovos, a 25-year-old novice lawyer. \"This amount is probably a privilege for the majority of youth near my age. We truly marginally survive,\" Kolovos said. Greece\'s three-party government insists there is no alternative to the harsh austerity programme demanded by the country\'s creditors in return for vital loans to stave of bankruptcy. Successive cuts to salaries and pensions over the past three years have angered Greeks who have frequently taken to the streets to demonstrate their frustration. The government has pledged to remedy some of the cuts when the economy limps back into growth next year -- a prospect that had been originally forecast for this year. Facing a sixth year of continuous recession, the heavily indebted country has been relying on international rescue packages to avoid bankruptcy and get its economy back on track. Since 2010 the European Union and the International Monetary Fund have committed 240 billion euros ($320 billion) overall in rescue loans to Greece. Auditors representing Greece\'s EU, European Central Bank and International Monetary Fund creditors are expected in Athens next week to assess the progress of its programme. Their report will determine whether Athens will receive a scheduled slice of 2.8 billion euros from its international creditors due in February. Among its obligations to its creditors, Greece must eliminate 25,000 civil service jobs this year, a measure set to cause further union trouble. The government has seen its parliamentary majority erode after adopting in November a new 18.5-billion-euro round of spending cuts and other reforms by 2016. The coalition now has 163 deputies in the 300-seat chamber.