Story highlights 94 officers injured after being hit by stones and an unknown substance, police say

At least seven police cars were set ablaze

Protesters are rallying against policies "responsible for mass joblessness"

(CNN) A massive anti-austerity rally in Germany turned violent Wednesday when protesters clashed with police at the opening of the new European Central Bank headquarters.

Frankfurt police said they used water cannons to disperse protesters after attacks on officers, firefighters, a police station and the Old Opera House.

At least 94 officers have been wounded, police said. Some suffered injuries when stones were thrown at them, and about 80 were hurt when they were attacked with a substance similar to pepper spray, police said.

Those affected by the substance had respiratory problems and eye irritation and needed treatment, police said. The substance quickly dissipated, and the place where it was discharged was not cordoned off.

The damage included at least seven police cars that were set on fire.

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