Workers at half a dozen Amazon distribution centres in Germany and one in Italy walked off the job on Friday in a protest timed to coincide with "Black Friday" to demand better wages from the American online giant.

In Germany, Ver.di union spokesman Thomas Voss said some 2,500 workers were on strike at Amazon facilities in Bad Hersfeld, Leipzig, Rheinberg, Werne, Graben and Koblenz. In a warehouse near Piacenza, in northern Italy, some workers walked off the job to demand "dignified salaries".

The German union has been leading a push since 2013 for higher pay for some 12,000 workers in Germany, arguing Amazon employees receive lower wages than others in retail and mail-order jobs. Amazon says its distribution warehouses in Germany are logistics centres and employees earn relatively high wages for that industry.

The strikes in Germany are expected to end on Saturday.

The Italian action, a one-day strike, was hailed by one of the nation's umbrella union leaders, the UIL's Carmelo Barbagallo, as having "enormous symbolic value because it's clear that progress, innovation and modernity can't come at the expense and the interests of workers".

The chief of the CISL umbrella labor syndicate, Annamaria Furlan, called on Amazon to work with unions for "proper industrial relations, employment stability and dignified salaries."

The Italian strike at the facility near Piacenza was called for permanent workers. The unions advised workers who are on short-term, work-on-demand contracts to stay on the job, so they would not risk losing future gigs.

Amazon says it has created 2,000 full-time jobs in Italy, where unemployment remains stubbornly high.

Amazon's head of personnel at the Piacenza-area centre, Salvatore Iorio, told Italy's Sky TG24 TV on Friday that despite the strike, the facility was keeping "our commitment to serve our clients".

Asked about union complaints that workers there did repetitive physical tasks to the point of experiencing health problems, Mr Iorio said the company "balances" positions at work areas to avoid any such problems.

AP