Speaking after meeting climate activist Luisa Neubauer in Berlin on Friday, Kaeser told journalists he had offered her a seat on the supervisory board of the group's new Siemens Energy division. Neubauer did not join the news conference.

Siemens' contract to provide signalling technology to the coal mine's railway is worth 18 million euros ($A29 million), Kaeser said.

The Australian government last year approved the construction of a new coal mine in Queensland by Adani that is expected to produce 8-10 million tonnes of thermal coal a year.

Australia is one of the world's largest carbon emitters per capita because of its reliance on coal-fired power plants.

The demonstrations, organised by the German branch of the Fridays for Future environmental youth movement, took place in several German cities, including Munich, where the firm is headquartered.

Protesters said they handed over a petition signed by 57,000 people during the hundreds-strong Munich demonstration.

Australian climate activists have for years been voicing their opposition to the mine, which would yield up to 60 million tons of coal per year.

Across Australia, more than 10 million hectares of land have burned since the bush fire season started in September, which is early for the season. At least 26 people have died and several thousand homes destroyed.

Australian Associated Press