The event was put off until November 1-2 to "offer time for the submission of effective studies and projects" for the reconstruction effort, the committee charged with planning the meeting said in a statement.
The divided country's eastern administration last month invited the "international community" to attend the conference in Derna, the coastal city where a September 10 flash flood devastated large areas and killed thousands.
The authorities later said that the conference would draw in international companies, and on Sunday the committee said the postponed event would be held in both Derna and the eastern city of Benghazi.
The North African country has been wracked by fighting and chaos since a NATO-backed uprising toppled and killed veteran dictator Moamer Kadhafi in 2011.
Libya is now divided between an internationally recognised Tripoli-based administration in the west, and the one in the disaster-stricken east backed by military strongman Khalifa Haftar.
- 'Separate efforts' -
The United States on Friday called on Libyans to set aside their political differences and agree on a framework to channel aid to eastern towns.
"We urge Libyan authorities now to form such unified structures -- rather than launching separate efforts -- that represent the Libyan people without delay," US special envoy Richard Norland said in a statement.
Despite a wave of nationwide solidarity since the flood, there has been no show of support for the proposed conference from the Tripoli-based government of interim Prime Minister Abdulhamid Dbeibah.
Jalel Harchaoui, a Libya specialist at the Royal United Services Institute, on Sunday said the eastern authorities were facing a "largely predictable setback," adding that "they will have no choice but to somehow work with the Tripoli authorities."
On Wednesday, the eastern authorities had announced the creation of a fund for the reconstruction of Derna and other areas affected by the flooding.
They did not indicate how the new fund would be financed, but Libya's House of Representatives, also based in the east, has already allocated 10 million dinars ($2 million) for reconstruction.
On Friday, the eastern administration announced that they had begun compensating residents affected by the floods, distributing cheques to the mayors of the stricken towns.
During talks with the European Commission, UN envoy Abdoulaye Bathily on Thursday said he had called for funds delivered to Libya to be monitored.
"I... emphasised the need for a joint assessment of reconstruction needs of storm-affected areas to ensure the utmost accountability in the management of reconstruction resources," he said.
According to the latest toll announced by the eastern authorities on Tuesday, at least 3,893 people died in the disaster.
International aid groups have said 10,000 or more people may be missing.
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