Turkish police on Wednesday fired tear gas and rubber bullets and detained dozens of protesters after authorities banned May 1 rallies at Istanbul's historic Taksim Square.
More than 40,000 police were deployed across Istanbul, blocking even small sidestreets with metal barriers in an attempt to prevent protesters gathering.
Police clashed with demonstrators near city hall in the Sarachane district, firing tear gas and rubber bullets to stop protesters breaching barricades, AFP reporters said.
According to media reports, at least 150 people had been detained by midday, but authorities did not confirm the figure. AFP reporters saw many people being arrested.
Some were detained trying to enter Taksim Square.
Tall metal barriers were put up around the square, where authorities have banned rallies since 2013, when it was the focus of demonstrations against President Recep Tayyip Erdogan's government.
Taksim was a rallying ground for May Day celebrations until 1977, when at least 34 people were killed during demonstrations. Authorities opened it up again in 2010, but it was shut again after the 2013 protests.
In the Besiktas district, police detained at least 30 left-wing protesters who were shouting "Taksim cannot be banned", an AFP journalist.
One protester was dragged along the ground by police and his group detained.
Another 30 people were detained in the Sisli district.
The MLSA rights group said several journalists were pushed to the ground during the troubles.
'Taksim belongs to workers'
Main roads across Istanbul were closed to traffic while public transport including ferries and subway trains were halted because of the security clampdown. Landmarks such as the Topkapi palace were cordoned off.
Interior Minister Ali Yerlikaya said Taksim would be out of bounds for rallies to stop "terrorist organisations" using it for "propaganda".
Turkey's main opposition Republican People's Party (CHP) and unions had pressed the government to open the square for labour rallies but Erdogan warned on Tuesday against any provocation.
CHP leader Ozgur Ozel, accompanied by Istanbul's mayor Ekrem Imamoglu and labour unions, gathered at the Sarachane neighbourhood.
"We will keep on fighting until Taksim is free," Ozel said. "Taksim belongs to the workers."
Addressing the police, Ozel declared: "These workers are not your enemies Our only desire is for the day to be celebrated as a festival. We do not want conflict."
In 2023, Turkey's top constitutional court ruled that the closure of Taksim Square for protests was a violation of rights.