Hundreds of angry Siemens workers protested at the industrial behemoth's historic Berlin factory Friday, in the first revolt against a mass jobs cull that unions have vowed to resist with all their might.

"We are Siemens and we aren't going anywhere," the crowd chanted, a day after the firm announced it would slash some 6,900 positions globally, mainly at its troubled power and gas unit.

Germany will account for almost half of the job losses.

Nearly 600 jobs will disappear in the German capital alone, including at the sprawling Dynamowerk site which, among other things, makes the huge gas turbines that have fallen out of favour as countries switch to renewable energy.

The demo was called by Germany's powerful IG Metall union, which has slammed the layoffs as "unacceptable" and pledged to put up fierce resistance.