The third summit of what France has called the coalition of the "willing and able" brings together leaders including Polish Prime Minister Donald Tusk, NATO Secretary General Mark Rutte, Italian Prime Minister Giorgia Meloni and Turkish Vice President Cevdet Yılmaz.
"First and foremost (we will discuss) the immediate support for Ukraine," President Emmanuel Macron told reporters on Wednesday evening at a press conference with Zelenskiy.
"It must go on because it is necessary to continue the resistance."
Macron committed to a further two billion euros ($A3.4 billion) in French military support to Ukraine.
Zelenskiy said other partners could announce aid packages on Thursday.
The format aims to forge a role for Europe in any talks on ending the conflict.
While the US is not present, French officials say the summit's outcomes will be shared with the US administration.
The discussions will focus on how to strengthen Ukraine militarily to deter future attacks and how to monitor limited ceasefires over sea targets and energy infrastructure, as discussed at US-led talks this week in Saudi Arabia.
European efforts, led by Macron and British Prime Minister Keir Starmer, to create security arrangements for Ukraine are shifting from sending troops to considering alternatives as they face political and logistical constraints and the prospect of Russia and the US opposing their plans, officials have told Reuters.
A concept paper for the summit seen by Reuters refers to a possible future reassurance force in Ukraine away from the front line "as part of a future peace settlement and with support of the United States".
A reassurance force positioned in Ukraine would aim to offer security guarantees and deter future aggression from Russia.
"The objective is to allow Ukraine to keep the situation on the ground and resist the Russian aggression while building the credible elements to this lasting peace," Macron said.
Zelenskiy said he hoped there would be more clarity on which countries would eventually commit to such a force.
"We are expecting some new and strong decisions," he said.
"We need to move forward on security guarantee discussions and the presence in Ukraine of partner contingents.
"We will see what is possible and not possible to do. It's not simple and I think it's still too early."
Underscoring the difficulties, Ukraine and Russia accused one another on Wednesday of flouting a truce on energy strikes brokered by the US, and the European Union said it would not meet conditions set by Russia for a planned ceasefire in the Black Sea.
