Left-wing groups and trade unions are staging rallies across Europe on Friday to mark International Workers Day.

Most events are expected to be peaceful protests for workers' rights and world peace.

But May 1 regularly sees clashes between police and militant groups in some cities.

Here's a look at May Day events in Europe:

GERMANY

Police in Berlin say the traditional 'Walpurgis Night' protest marking the eve of May 1 was calmer than previous years.

Several thousand people took part in anti-capitalist street parties in the north of the city. Fireworks and stones were thrown at police, injuring one officer. Fifteen people were detained. Elsewhere in the German capital revelers partied "extremely peacefully," police noted on Friday morning.

TURKEY

Authorities determined to keep May Day protesters out of Istanbul's Taksim Square have stationed a small army of police with water cannons in and around the iconic spot.

The square is symbolic as the center of protests in which 34 people were killed in 1977. Taksim was also the focus of massive anti-government protests that rocked Turkey in 2013.

Turkish newswires say 10,000 police are ready to enforce the government's ban on protests in the square Friday. Clashes are also expected in other Turkish cities.

The demonstrations are the first large scale protests since the government passed a security bill this year giving police expanded powers to crack down on protesters.