Thousands of Amazon workers went on strike in Spain and Germany on Tuesday in protest at their working conditions as the retail giant staged its Prime Day sales event, unions said.

In Spain, employees in San Fernando de Henares near Madrid—Amazon's biggest logistics centre in the country—were observing a second day of work stoppage which was due to continue on Wednesday.

Ana Berceruelo of the CCOO union told AFP that 1,200 workers were taking part—around 80 percent of the centre's workforce.

Spanish unions want a higher pay rise than the 1.1 percent proposed by Amazon and better working conditions.

But Amazon Spain said the participation figure given by the union was wrong.

"Today the majority of the centre's employees worked and handled our customers' orders," it said in a statement, without giving a detailed figure.

It claimed its workers had "a competitive salary, a complete package of benefits and programmes of innovative training."

In Germany, six sites were hit by a strike on Tuesday with the work stoppage due to continue on Wednesday at the Leipzig depot.

According to Verdi, the biggest German union in the services sector, 2,400 workers were taking part.

Amazon Germany was not immediately available for comment.

"The message is clear: when the online trade giant gets rich, it's on the back of the health of its employees," Verdi's Stefanie Nutzberge said in a statement.