Trump, speaking alongside UK Prime Minister Keir Starmer at his golf resort in Turnberry, Scotland, said the United States had provided $US60 million ($A92 million) for humanitarian aid and other countries would have to step up.
He said he discussed the issue with European Commission President Ursula von der Leyen on Sunday, and she told him European countries would step up their assistance very substantially.
He said he also planned to discuss the humanitarian situation with Starmer during his visit on Monday.
"We're giving a lot of money and a lot of food, and other nations are now stepping up," Trump said.
"It's a mess. They have to get food and safety right now."
Starmer agreed, saying: "It's a humanitarian crisis, right? It's an absolute catastrophe .... I think people in Britain are revolted at seeing what they're seeing on their screen."
Trump said he would not comment on a push by French President Emmanuel Macron to back Palestinian statehood.
Trump also criticised the Hamas militant group for not agreeing to release more hostages, living and dead, and said he had told Israeli Prime Minister Benjamin Netanyahu that Israel's approach would likely have to change.
"I told Bibi that you have to maybe do it a different way," Trump said, echoing similar comments made on Sunday.
Asked if a ceasefire was still possible, Trump said, "Yeah, a ceasefire is possible but you have to get it, you have to end it."
He did not elaborate on what he meant.
Trump underscored the importance of securing the release of hostages held by Hamas in the Gaza Strip, saying the Palestinian group had changed its position and was refusing to release more hostages.
Hamas has said it is willing to release hostages under a ceasefire agreement with Israel.
It submitted its response to a US-backed ceasefire proposal on Thursday at talks in Doha.
Hours later, Israel withdrew its delegation from the talks.
On Sunday, Trump said Israel would have to make a decision on next steps, adding, "I know what I'd do but I don't think it's appropriate that I say it".
Israel carried out an air drop and announced a series of measures over the weekend to improve access for aid, including daily humanitarian pauses in three areas of the Gaza Strip and new safe corridors for convoys.
United Nations agencies say those moves are not yet sufficient to alleviate famine-like conditions facing the enclave's residents.
On Monday, the Gaza health ministry said at least 14 people had died in the past 24 hours of starvation and malnutrition, bringing the war's death toll from hunger to 147, including 89 children, most in just the last few weeks.
Israel cut off all supplies to the Gaza Strip from the start of March, reopening the territory with new restrictions in May.
Israel says it abides by international law but must prevent aid from being diverted by militants, and blames Hamas for the suffering of the Gaza Strip's people.
"Israel is presented as though we are applying a campaign of starvation in Gaza. What a bald-faced lie. There is no policy of starvation in Gaza, and there is no starvation in Gaza," Netanyahu said on Sunday.
