Greek unions are staging a 24-hour walkout, paralysing services and snarling public transport over labour legislation that will allow greater job flexibility.

Civil servants, hospital workers, school teachers and dock workers joined the strike on Thursday, which also shut down the Athens subway and left buses operating on reduced hours.

A key part of the bill, which is expected to be approved by parliament, is that private sector staff will be allowed to work at more than one employer daily.

Businesses will also be able to require staff to work six days a week in an emergency.

Opposition parties and unions have accused the conservative government of empowering employer exploitation in a poorly-supervised labour market where many workers are afraid of losing their jobs.

The labour ministry says the purpose of the legislation is to "boost employment" and "increase the number of viable and justly paid jobs."

The bill also forbids strikers to prevent other staff from working during a walkout, and disallows layoffs linked to discrimination.

On Wednesday, the entrance of an Athens building housing the private office of Labour Minister Adonis Georgiadis was daubed with red graffiti calling him "scum".

The government passed a law in July allowing people to continue working up to the age of 74, seven years beyond the official retirement age.

Prime Minister Kyriakos Mitsotakis has vowed to reduce unemployment in Greece, currently at 10.8 percent, to eight percent by 2027.