UN Secretary-General Antonio Guterres urged Israel to allow rapid and unhindered aid access and told the General Assembly he would launch a full humanitarian appeal for funding as soon as possible.
"If there is a hell on earth, it is the lives of children in Gaza today," Guterres said.
"The hostilities have caused serious damage to vital civilian infrastructure in Gaza, including roads and electricity lines, contributing to a humanitarian emergency. Crossings into Gaza have been closed and power shortages are affecting water supplies," Guterres added.
Hundreds of buildings and homes have been destroyed or damaged, Guterres said, and airstrikes have damaged several hospitals. Some 50,000 people were seeking shelter in UN schools, mosques and other places with little access to water, food, hygiene or health services, Guterres added.
"The needs in Gaza in particular are immense," Thomas-Greenfield said. "We hope the international community will step up to meet the humanitarian needs on the ground."