The EU on Thursday said it had released €33 million (Dh143.9m/$39.2m) to finance initial emergency aid for Lebanon.
It also sent resources including an Italian hospital ship to help relief work in Beirut, which was devastated on Tuesday by two explosions.
A donor conference is also planned to gather more funds for rebuilding after an assessment of what is required, an EU source said.
The release of the funds should cover the immediate needs of emergency services and hospitals in the Lebanese capital, the European Commission said.
Commission President Ursula von der Leyen spoke with the Lebanese Prime Minister, Hassan Diab, on Thursday about EU assistance.
In a letter to the 27 EU members, Ms Von der Leyen and Charles Michel, President of the European Council, called on member states to "contribute to the road to recovery that lies ahead".
"We invite you to intensify your support to Lebanon on the immediate needs, but also with a view to the longer-term reconstruction of the country," they wrote.
"To ensure efficiency and swift delivery, we stand ready to ensure the synergy of the aid that you and the EU as a whole will provide to Lebanon, through a co-ordination mechanism that the EU institutions will put in place."
They reminded the member states of the "strong partnership" between the EU and Lebanon, "a country of strategic importance, which hosts the largest number of refugees per capita".
"We have a common interest in acting now to limit the fallout of this tragedy," Ms von der Leyen and Mr Michel wrote.
European countries have reacted quickly. The Italian navy hospital ship has medical equipment and helicopters for evacuation.
Italy has also sent 250 firefighters specialising in search and rescue, an EU source said.
