The Christian Democrat of the European People's Party is promising European parliamentarians she will put climate and social issues at the heart of her program over the next five years as she seeks to gather the requisite 374 votes out of 747.

Von der Leyen was a last-minute candidate to succeed Jean-Claude Juncker as part of a package of top jobs that EU leaders decided on early this month.

Under the package, the free-market liberal Renew Europe group got Belgian Prime Minister Charles Michel as Council President and the Socialists won the top parliament job.

However parliamentarians have voiced their anger that they were sidelined in the appointment process: their candidates for the Commission post were all rejected by the EU leaders.

"This is about much more than a personnel issue," senior Social Democrat European lawmaker Katarina Barley told ZDF television Tuesday. "In the election campaign, we called for the EU to become more democratic - including with the 'lead candidate' principle. We think it is very important that the Council cannot simply throw that in the trash with loud applause from right-wing populists."

Von der Leyen would become the first woman to lead the EU's executive.

In her speech to the parliament on Tuesday, she immediately addressed what she sees as the biggest challenge - climate change.

"I want Europe to become the first climate-neutral continent in the world by 2050," she said, adding she would work out a "a green deal for Europe in the first 100 days" of her office.

Australian Associated Press