Israeli tank shellfire has killed at least 45 Palestinians in Khan Younis, according to the Hamas-run health ministry in Gaza.
Hundreds of others have been injured – with “dozens of critical cases” arriving at a medical complex.
It is feared that the number of fatalities will rise.
The strikes took place as people waited for aid trucks in the southern Gaza city.
“Emergency, intensive care, and operating rooms are experiencing severe overcrowding,” a statement said.
Officials say medical staff “are operating with limited supplies of life-saving medicines” – with the ministry renewing an “urgent appeal” to increase aid.
Hours earlier, Donald Trump had joined other G7 leaders to call for a “de-escalation of hostilities in the Middle East, including a ceasefire in Gaza”.
The Israeli military is yet to comment on this incident.
On Monday, Gaza’s health ministry said at least 34 people were shot dead near food distribution centres.
This was the highest reported daily total since Israel and US-backed aid centres opened last month, with thousands of Palestinians moving through Israeli military-controlled areas to reach them.
