AFP/ Tehran

Turkish police on Friday put Istanbul under a security shutdown to thwart unauthorised demonstrations on a tense May Day, as tens of thousands of labour activists turned out worldwide to defend their rights at a time of austerity.

Roads to the centre of Istanbul were closed and public transport severely restricted in Istanbul with the Turkish authorities seeking to only allow the most tightly-controlled protests by unions.

The usually traffic-clogged streets in Istanbul centre were eerily quiet as police blocked all vehicle access to Taksim Square, the traditional focus for protests in the city.

By contrast, thousands of people packed into the centre of Athens in response to a call from public and private unions.

In Moscow, some 140,000 workers and students paraded on Red Square, waving Russian flags and balloons, a spectacle harking back to Soviet times.

Around 2.5 million Russians were expected to turn up for May Day demonstrations across Russia, said the ruling party United Russia.

Meanwhile, tens of thousands of people were expected to protest later in the afternoon in Milan against the opening Friday of the Expo 2015 in Italy's financial centre.

Opponents of the project have accused the authorities of a needless waste of public funds by hosting the show at a time of austerity.

In South Korea, tens of thousands of workers held May Day rallies, vowing to wage an "all-out general strike" if the government pushes through with planned labour reforms.

- '20,000 police' -

Several hundred people turned out for an initial protest under heavy police surveillance in Istanbul's Besiktas district on the Bosphorus, shouting "Long Live May 1!" and "shoulder to shoulder against Fascism!"

A small group of a few dozen Communist protesters who tried to protest in the centre of Taksim Square were immediately surrounded by police who roughly arrested several people.

President Recep Tayyip Erdogan's administration -- shaken by weeks of deadly anti-government protests in May-June 2013 centred on Taksim Square -- is hugely nervous about public demonstrations ahead of June 7 legislative elections.

Taksim Square has been a flashpoint for clashes on Labour Day since dozens of people were killed there on May 1, 1977 when modern Turkey was going through one of its most turbulent periods.

"In 1977 there was a massacre. We simply want to the there (on Taksim) to commemorate that date. We cannot do it any other way, it is too symbolic for us," Umar Karatepe, a leader of the DISK labour confederation, told AFP.

"The president, this man who usurps all our rights, cannot tell us that we are not able to celebrate May 1, it's unacceptable."

Turkish media said 20,000 police had been deployed in Istanbul backed up by 62 water cannon trucks that the police are happy to use in case of clashes.

The blocking of traffic left some locals with long walks to carry out their business while travellers carrying heavy luggage were stranded as they sought a ride to the airport.

In an apparent bid to discourage protests, the city's main metro line was halted well before Taksim and services on the city tram service were stopping halfway.

Taksim Square, usually thronged with thousands of people in the day, was deserted save for police, journalists and plain clothes security agents.

Several ferry services from the Asian side of the Bosphorus were  suspended to prevent people from crossing to join protests on the European side.

Private helicopters were also banned from taking to the skies to give the airspace to police choppers.

This is the first May Day in Turkey, a national holiday in the country, to be marked after parliament passed a controversial security bill this year giving the police greater powers to crack down on protests.