A protester takes aim at riot police with a slingshot in Istanbul. (Murad Sezer/Reuters)

Protesters in Istanbul defied a government ban and marched in the streets on May Day, determined to mark International Workers' Day, according to media reports.

Photos from Istanbul show them being met by security forces with water cannons and tear gas. The Progressive Lawyers Association said about 40 people were hospitalized and 160 detained, the Reuters news agency reported.

Authorities had previously shut down part of the public transportation system and put up barricades, according to Reuters. Prime Minister Recep Tayyip Erdogan had said unions couldn't march in protests today because such demonstrations — as well as social-media leaks that suggest corruption and malfeasance in his administration — are undermining him.

Riot police used water cannons and tear gas to disrupt crowds marching towards Istanbul's Taksim Square in defiance of a government ban on May Day or International Workers' Day. (Reuters)

May 1, a day on which people around the world celebrate spring as well as International Workers' Day, has major significance to many in Turkey. In 1977, hundreds of thousands of people gathered in Istanbul's Taksim Square, and 34 were killed when shots were fired into the crowd from a nearby building. May 1 was declared a national holiday in 2009.

Demonstrators clash with riot police in Istanbul on Thursday. (Javier Manzano/For The Post)

A protester is arrested. (Javier Manzano/For The Post)

Demonstrators clash with police in Istanbul. (Javier Manzao/For The Post)

A protester holds an improvised bomb in Istanbul. (Burak Kara/Getty Images)

Protesters try to shield themselves from tear gas. (Cevahir Bugu/Reuters)

Protesters set up barricades and wave flags amid tear-gas smoke in Istanbul. (Murad Sezer/Reuters)

A protester applied cream to his face to protect against tear gas. (Umit Bektas/Reuters)

Protesters clash with riot police using water cannons and tear gas. (Ulas Yunus Tosun/European Pressphoto Agency)

A riot police officer amid tear gas in Istanbul. (Murad Sezer/Reuters)

Riot police aim water cannons at protesters in Istanbul. (Murad Sezer/Reuters)