A massive police intervention may be in order if demonstrations on and around May 1 devolve into violence, as has happened previously, Berlin's state interior senator warned Saturday.

Senator Iris Spranger said that the initial strategy would be one of peace and openness. "But we will of course intervene and the police will of course intervene massively if there are riots," she told rbb24 Inforadio on Saturday.

Some 6,000 police officers are on the street, she said, with Berlin police backed up by federal police and officers from other states. "Of course we know that violence can and most likely will occur," she said.

Spranger expects up to 50,000 people to attend peaceful demonstrations and public festivals to mark May 1, although the gatherings could see extremist activity, she said.

Germany celebrates labor day on May 1, often with street fairs, demonstrations and protests. However, there have also been occasional outbreaks of violence and clashes between protesters and police in Berlin.

Several demonstrations and rallies are due to take place in Berlin on Saturday, including a left-wing radical street party in Rigaerstrasse and a left-wing demonstration in the Wedding neighborhood. A further protest is expected in Kreuzberg against plans to open a police station at the Kottbusser Tor square. Meanwhile in the evening, a demonstration is planned to "smash the patriarchy."