Police used tear gas to disperse demonstrators in downtown Athens on Wednesday during a rally that attracted some 20,000 people protesting government-imposed austerity measures.

Authorities said five people were arrested and one police officer was slightly injured in the unrest. The rally was held as part of a 24-hour general strike organised by the two leading labour unions -- the GSEE and the ADEDY.

The action blocked public transport, ports, schools, public offices as well as private businesses. Flights halted in the afternoon, while hospitals were only treating emergencies.

The strike coincides with the start of a crucial inspection by a team of EU and IMF experts in Athens.

They will spend around a week in the country to assess whether Greece's debt is sustainable and whether it has made enough progress to receive the fifth 12 billion-euro tranche of a 110 billion-euro bailout package.