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.

"We will take to the streets and we expect the mobilisation to be spectacular because you can see the level of solidarity between the employees," union member Kris told AFP, declining to give his last name.

"I can tell you that the mood in the meetings is very combative," he added, sporting the union's red jacket emblazoned with the slogan "Siemens metal workers. We fight like bears".

Siemens unveiled the layoffs as part of a major overhaul as it grapples with falling orders in a changing energy landscape.

But the "painful cuts" Siemens says are necessary have sparked outrage after the conglomerate -- which also makes trains, wind turbines and medical equipment -- only last week reported flourishing financial results.

Net profit for 2016-2017 rose by 11 percent year-on-year to 6.2 billion euros, it said.

As well as the layoffs in Germany, Siemens plans to close its sites in Goerlitz and Leipzig, both in the country's economically weaker former communist east.

Some 1,100 jobs are also set to go in the rest of Europe, while the United States will see 1,800 layoffs.

Martin Schulz, the leader of the Social Democratic Party that is set to go into the opposition after September's general election, called the job cuts an "outright scandal".

"It's a slap in the face for all those employees who worked so hard for the company and its profits