Alessandro Mrakic, head of the UNDP Gaza Office, said work had started to remove the solid-waste mound that has overtaken the once busy Fras Market in the Palestinian enclave's main city.
He put the volume of the dump at more than 300,000 cubic metres and 13 metres high.
It formed after municipal crews were blocked from reaching the Gaza Strip's main landfill in the Juhr al-Dik area - adjacent to the border with Israel - when the war in the enclave began in October 2023.
The area in Juhr al-Dik is under full Israeli control.
Over the next six months, UNDP plans to transfer the waste to a new temporary site prepared in the Abu Jarad area south of Gaza City and built to meet environmental standards.
The site covers 75,000 square metres and will also accommodate daily collection, Mrakic said in a statement sent to Reuters.
The project is funded by the Humanitarian Fund and the European Union's Civil Protection and Humanitarian Aid Operations.
Some Palestinians sifted through the rubbish, looking for things to take away, but there was relief that the market space would eventually be cleared.
"It needs to be moved to a site with a complex of old waste, far away from people. There's no other solution. What will this cause? It will cause us gases, it will cause us diseases, it will cause us germs," elderly Gazan Abu Issa said near the site.
The Gaza Municipality confirmed the start of the relocation effort in collaboration with the UNDP, calling it an urgent step to contain a worsening solid-waste crisis after about 350,000 cubic metres of rubbish accumulated in the heart of the city.
Fras Market, an historical quarter that before the war served nearly 600,000 residents with items ranging from food to clothes and household tools, has been buried under rubbish for more than a year.
Amjad al-Shawa, head of the Palestinian NGOs Network and a liaison with UN and international agencies, said the dump had fuelled "serious health and environmental problems and the spread of insects and illnesses".
"It is a symbol of the war that continued for two years," he told Reuters.
"Its removal may give people a sense of hope that the ceasefire (agreed last October) is moving forward."
Shawa said the waste would be transported to a transitional site near the former Netzarim settlement in the centre of the Gaza Strip until Israeli forces withdraw from eastern areas and municipal access to the permanent landfills can be restored.
UNDP said it had collected more than 570,000 tons of solid waste across the Gaza Strip since the war began as part of its emergency response to avert a further deterioration in public health conditions.
The number of temporary dump sites has decreased from 141 to 56 as part of efforts in 2024-25 to remove smaller dumping sites, a UNDP report last December said.
"However, only 10 to 12 of these temporary dumping sites are accessible and operational, and Gaza's two main sanitary landfills remain inaccessible. The environmental and public health risks remain critical," it added.
