A UN agency said Thursday rebuilding war-wracked Gaza will cost an estimated $30 billion to $40 billion and require an effort on a scale unseen since World War II.

"The United Nations Development Programme's initial estimates for the reconstruction of... the Gaza Strip surpass $30 billion and could reach up to $40 billion," said UN assistant secretary-general Abdallah al-Dardari.

"The scale of the destruction is huge and unprecedented... This is a mission that the global community has not dealt with since World War II," Dardari told a press conference in the Jordanian capital Amman.

He added that if Gaza's reconstruction were to be carried out through the normal process, "it could take decades, and the Palestinian people do not have the luxury of waiting for decades".