Greece's largest union on Wednesday staged a 24-hour walkout that hit public transport and ferry services to the islands.

The General Confederation of Greek Workers called the strike to protest the cost of living and demand higher wages and the restoration of collective bargaining.

The action knocked out ferry services to the Aegean and Ionian islands, and the Athens metro. Police estimated around 4,000 people also demonstrated in central Athens in support of the strike.

Hospital doctors also went on strike, while taxis and buses held work stoppages in support.

Another strike by civil servants has been called on May 21. This was the second such strike in six weeks, with social discontent against the conservative government of Kyriakos Mitsotakis mounting less than a year after the re-election of his New Democracy party.

Union leaders have criticised ongoing labour market deregulation and low wages at a time when the economy is growing. But the ruling party remains ahead of the opposition in the polls, less than two months before June 9 European Parliament elections.