Two Palestinian toddlers with sunken eyes and emaciated faces, one in a yellow cardigan and the other in a stripy top, were lying side by side on a bed in a Gaza clinic, their thin, bony legs protruding from diapers that looked too big for them.

This was the scene on Monday at Al-Awda health centre in Rafah, southern Gaza, where nurse Diaa Al-Shaer said children suffering from malnutrition and from a range of diseases were arriving in unprecedented numbers.

The toddler in the yellow cardigan, Ahmed Qannan, weighed 6 kg (13.2 lb), half of his pre-war body weight, according to his aunt, Israa Kalakh, who was by his side.

"His situation worsens each day. God protect us from what is coming," she told Reuters.

Nearly five months into Israel's air and ground assault on the Gaza Strip and resulting mass displacement, acute shortages of food have led to what the United Nations is describing as a nutrition crisis, part of a wider humanitarian catastrophe.

Gaza's Health Ministry said on Sunday that 15 children had died of malnutrition or dehydration at Kamal Adwan hospital in Beit Lahiya, northern Gaza, the part of the enclave where the lack of food is most extreme.

"The unofficial numbers can unfortunately be expected to be higher," said World Health Organization spokesperson Christian Lindmeier.

The worsening hunger crisis has intensified criticism of Israel on the world stage, including from US Vice President Kamala Harris, whose country is Israel's staunchest ally. She said on Sunday that people in Gaza were starving, calling on Israel to do more to significantly increase the flow of aid.

Dr Ahmad Salem, who works in the hospital's intensive care unit, said one of the factors in the high number of child deaths there was that new mothers were themselves malnourished.

Deliveries of food aid to the whole of Gaza are falling far short of what is needed, and the problem is worse in the north because the only crossings where Israel allows trucks to pass are in the south.