Police in Athens have clashed with groups of demonstrators as thousands marched through the city in protest at government austerity measures. Dozens of hooded youths hurled stones and petrol bombs at police, who responded with rounds of tear gas. The march, called by Greek unions, is part of a 24-hour strike that has brought most public services to a halt and paralysed transport networks.Police said there were several arrests and two police officers were injured. Reports say at least 10,000 people took part in the march, which was largely peaceful. Thousands also took part in protests in the northern city of Thessaloniki. The strike was called after the Greek government proposed a new austerity package to try to reduce the budget deficit and ease the country's crippling debt crisis. Unions say the policies are making Greece's problems worse.