Storm Daniel pummelled the Thessaly region in central Greece for three days last week at the end of the hottest summer ever recorded in the country.

"Our thoughts are with all the women, men and children who are courageously withstanding these disasters and we mourn the lives lost," EU Commission Chief Ursula von der Leyen said after meeting Greek Prime Minister Kyriakos Mitsotakis in Strasbourg.

"Α lot of investment will be necessary to rebuild but a lot of immediate aid will be necessary to restore livelihoods."

The commission would be "quick and flexible" and mobilise all the resources that could be deployed to help areas devastated by the floods, she added.

Greece could tap "up to 2.25 billion euros", she said, while the Commission also stood ready to assess a Greek request for further support under the solidarity fund.

If all member states agree to top up the bloc's solidarity fund, the European Union could also make up to 400 million euros available to Greece next year, she said.

The unprecedented natural disaster in Greece has profoundly damaged people's lives and dealt a massive blow to agricultural production, Mitsotakis said, standing alongside von der Leyen and showing a picture of an inundated Greek village.

"Our number one priority is to make sure that these people can actually return to their houses, that businesses can start operating again and we count on EU support to be able to achieve that," Mitsotakis said.

He also called on Europe to spend more to help countries deal with the climate change.

The EU's solidarity and emergency aid reserve, which helps European countries in an emergency, has a maximum annual budget of 1.2 billion euros ($1.29 billion).

The European Commission warned on Tuesday that the EU urgently needs more funding to respond to climate change-fuelled crises after its emergency aid reserve was exhausted in both 2021 and 2022. ($1 = 0.9334 euros)