Chinese appliances giant Midea moved a step closer to fulfilling its ambition to acquire German industrial robotics firm Kuka with a deal raising its stake to more than 35 percent.

Kuka's biggest German shareholder, technology company Voith, said on Sunday that it had decided to take up Midea's offer of 115 euros ($128) per share and sell its 25.1 percent stake to the Chinese group, German news agency DPA reported.

Midea has already amassed a stake of 13.5 percent in Kuka and in mid-May launched a cash offer valuing the company at more than four billion euros.

Initially, Midea's offer will run July 15, but Kuka's management is recommending shareholders accept it and has signed a long-term investor contract with the Chinese firm until 2023.

Nevertheless, critics are worried about German know-how and technology being sold into Chinese hands.

A growing list of German companies, such as Kion, Putzmeister and KraussMaffei have come under Chinese ownership in recent years.

Kuka, based in the German city of Augsburg, describes itself as one of the world's leading manufacturers of industrial robots and also offers automated systems for manufacturing.

The powerful IG Metall trade union had pushed for the Voith stake to remain in German hands -- but no competing buyer came forward.