Unions have launched another general strike against austerity measures in Greece, amid predictions unemployment in the crisis-hit country will reach 30% this year.

Today's 24-hour protest by unions representing private and public sector workers has disrupted flights, halted ferries and crippled public services.

The strikes are a renewed confrontation between labour groups and the conservative-led government over policies aimed at curbing Greece's overspending.

State-run schools, most public transport services, and even farmers markets also stopped running during the strike.

In Athens, up to 3,000 police officers were on duty for union-organised street rallies due to start in mid-morning.

Greek Prime Minister Antonis Samaras has won praise from bailout lenders for pushing through major cost-cutting measures after forming a three party coalition last June.

French President Francois Hollande was in Athens yestereday to express the "support of France and trust in the actions of (Greece's) government in recent months."

But a new round of tax increases this year and a surge in unemployment to 27% have angered unions, as Greeks battle a rapid increase in poverty and face a sixth year of recession. In recent weeks, the Samaras government has twice used rare emergency powers to force an end to strikes by workers on ferry services and the Athens subway.

Unions are also angry at a government decision to scrap collective wage agreements across the public sector as part of an overhaul of state pay scales that will usher in further salary cuts.

Unemployment is expected to reach an alarming 30% this year, while national output will contract a further 4.1%, according to a study by a government funded research agency published last week.