The devastating storm, which hit the island nation late last month, killed at least 639 people and affected more than 2 million others -- about 10 percent of the population -- causing extensive damage to homes, roads, bridges, industries and agriculture.

Some 200 people are still missing.

The UN's top envoy to the country, Marc-Andre Franche, announced plans for a $35.3-million emergency fund which he said was needed to feed and cater to the basic needs of 658,000 people who have been worst affected.

The fund excludes reconstruction of damaged infrastructure or personal property and focuses solely on immediate basic needs.

Franche said $9.5 million had already been secured, with the European Union, Switzerland, Britain and the United States among the donors pledging funds.

The United Nations urged member states and other donors to help raise the remaining $25.8 million for the daunting recovery and reconstruction effort.

The natural disaster, which President Anura Kumara Dissanayake has described as the most challenging for his country, struck as Sri Lanka was emerging from its worst economic crisis.

It defaulted on its $46-billion external debt in April 2022, and secured a $2.9-billion bailout from the International Monetary Fund in early 2023, having only stabilised the economy earlier this year.

"The disaster is hitting the country at a moment when around 25 percent of Sri Lankans still live in poverty," Franche told reporters in Colombo.

Ongoing monsoon rains continue to pose a hazard with continued landslide warnings, the UN said.