Germany's economy minister urged Thursday the EU to shield its key industries from foreign investors after Chinese appliance giant Midea made a controversial bid for German robotics group Kuka.

Sigmar Gabriel, who is also vice chancellor, has recently expressed his disapproval of Midea's takeover bid.

Writing a guest editorial for Friday's edition of business weekly WirtschaftsWoche, Gabriel said the EU should be protective of not only its security and defence sectors.

"We should discuss whether we should also take into consideration the industrial interests of the EU vis-a-vis those of investors, for sectors that are strategic for the future of the European economy," he wrote.

"The areas where the seeds of prosperity and value creation of tomorrow are sown have changed. We must take this change into account," argued the centre-left Social Democrat.

Chinese appliance giant Midea -- best known for its washing machines and air conditioners -- last month launched a takeover offer for Kuka.

It is seeking at least a 30 percent stake in a deal that values Kuka at 4.6 billion euros ($5.2 billion). Midea already holds a 13.5 percent stake in Kuka.

In what appeared to be a veiled attack at China, whose state-run enterprises have been going on a shopping spree in Europe, Gabriel wrote that "we have to ask ourselves seriously whether we want investors from third countries who move into our market economy using state resources."

"I am not ready to sacrifice jobs and companies on the altar of an open European market," he added.

During a press conference on Wednesday, Gabriel had criticised investments made by "companies from countries that have not even themselves opened their markets", in a direct attack at China.

Gabriel's comments come just ahead of Chancellor Angela Merkel's visit on Sunday to Beijing.

The German leader has so far not commented on the Kuka case.