Turkish police fired tear gas and water cannon at hundreds of stone-throwing May Day protesters, after they defied a ban and tried to march on Istanbul's Taksim Square.
Thousands of police manned barricades and closed streets to stop demonstrations at Taksim, a traditional rallying ground for leftists that saw weeks of unrest in 2013.
Riot police unleashed water cannon and chased protesters down side streets in the nearby Besiktas neighbourhood, where they fired off canisters of tear gas. Demonstrators lobbed stones and bottles at police and set off fireworks.
Istanbul police said around 140 people had been detained, although activists said the number was nearly double that.
The Istiklal shopping avenue leading to Taksim was deserted, with shops shuttered and metal barricades blocking off side streets. Police helicopters circled overhead. A usually bustling square lined with cafes and hotels, Taksim was filled with police buses, ambulances and satellite broadcast trucks.
Much of Istanbul's public transport had been shut down due to security concerns, and police helicopters circled over the city.
Critics say President Tayyip Erdogan and the government have become more authoritarian in the buildup to June elections. Erdogan has previously dismissed protesters as "riff-raff" and terrorists, outraged by the unrest in 2013 that brought unwanted international attention and posed the biggest challenge to his AK Party since it came to power in 2002.
He is aiming for a massive victory in June parliamentary polls, which would allow a change to the constitution and give him broad presidential powers.
The 2013 Taksim protests began as a peaceful demonstration against plans to redevelop Gezi Park, a leafy corner of the square. After a police crackdown the demonstration spiraled into weeks of nationwide protests against Erdogan's rule.