He again signalled the UN's refusal to join a new US-backed distribution plan.
Speaking to reporters, Guterres stressed, "Without rapid, reliable, safe, and sustained aid access, more people will die – and the long-term consequences on the entire population will be profound."
The UN and its partners have a plan to get the aid needed into Gaza, he said.
"The supplies – 160,000 pallets, enough to fill nearly 9,000 trucks – are waiting," Guterres said. “This is my appeal for life-saving aid for the long-suffering people of Gaza: Let's do it right. And let's do it right away.”