Ms. von der Leyen said that the first ship carrying aid could depart the E.U. nation of Cyprus for Gaza as soon as Friday, with more to follow on Sunday. But it was not immediately clear how or where the vessels would unload their cargo or how it would be distributed amid Israeli bombardment and attacks by hungry Palestinians on aid trucks.

Gaza does not have a functioning port, its coastal waters are too shallow for most vessels and U.S. officials have said it could take 30 to 60 days to set up the floating pier.

At a news conference in Cyprus, Ms. von der Leyen offered few details. Israel’s Foreign Ministry said in a statement on Friday that it supported a maritime corridor as long as goods are checked “in accordance with Israeli standards” before leaving Cyprus.

Despite the many questions, U.S. and European officials emphasized the urgent need to open new routes for aid into Gaza, where relief agencies say that 2.2 million Palestinians are facing extreme hunger amid Israeli airstrikes and ground attacks against Hamas. In a joint statement, Britain, the E.U. and the United Arab Emirates said the maritime corridor must “be part of a sustained effort to increase the flow of humanitarian aid and commercial commodities into Gaza through all possible routes.”

For months, the United States and others have warned that Israel was not allowing sufficient aid by land into Gaza. Those concerns have multiplied in recent days, as Palestinian health officials reported that some Gazan children had died of malnutrition and the United Nations warned that more than 570,000 people are facing “catastrophic levels of deprivation and starvation.”

Aid officials say that sea shipments — and a limited number of airdrops conducted by the United States and other nations — cannot make up for the lack of supply routes by land. Only about 100 relief trucks entered Gaza each day in February, on average, through the two open land routes, a fraction of what was going in before the war began in October. Israel has insisted on inspecting shipments into Gaza, arguing that they could be diverted by Hamas, but says it does not restrict how much aid gets in.

“We know the difficulties faced at the land borders in Gaza,” Ms. von der Leyen told reporters.

Mr. Cameron, in announcing that Britain would join the maritime effort, said in a social media post: “We continue to urge Israel to allow more trucks into Gaza as the fastest way to get aid to those who need it.”

Israeli officials have not said whether they would open more land routes into Gaza, as many aid agencies have called for, particularly into northern Gaza where relief deliveries have all but stopped because of insecurity.

Plans for the sea route began taking shape months ago. In November, President Nikos Christodoulides of Cyprus, announced an initiative to collect shipments in his country, inspect them at the port of Larnaca and sail them through a secure sea corridor to Gaza, about 240 miles away.

A spokesman for the Cyprus government, Konstantinos Letymbiotis, said that if initial shipments this weekend are successful, more deliveries would follow. He said it would take about 15 hours to make the journey, although he declined to say where the shipment would be delivered in Gaza, citing security concerns.

“As a European Union member at the heart of the region, Cyprus bears a moral duty to do its utmost to assist in alleviating the humanitarian crisis,” Mr. Christodoulides said on Friday.

Niki Kitsantonis contributed reporting.