The Gaza Strip will not be "a liveable place" by 2020 unless action is taken to improve basic services in the territory, according to a UN report.
Basic infrastructure "is struggling to keep pace with a growing population", the UN Country Team (UNCT) in the occupied Palestinian territory said.
It estimates Gaza's population will rise from 1.6m to 2.1m by 2020.
Israel imposed a blockade on Gaza after the Islamist movement Hamas seized power in the coastal territory in 2007.
Israel says the restrictions, which are policed with Egyptian co-operation, are necessary to prevent weapons reaching Hamas. Palestinians and human rights group denounce them as "collective punishment".
The UN report, "Gaza in 2020: A liveable place?", estimates the territory will need double the number of schools and 800 more hospital beds by 2020, and says it is already suffering from a housing shortage.
The report also says the coastal aquifer, the territory's only natural source of fresh water, may become unusable by 2016.
UN officials point to the difficulty of improving the situation given "the closure of the Gaza Strip, violent conflict, and the pressing need for Palestinian reconciliation".
"An urban area cannot survive without being connected," said Maxwell Gaylard, the UN Resident and Humanitarian Co-ordinator.
Gaza has no air or sea ports, and the economy is heavily dependent on outside funding and smuggling through tunnels under the Egyptian border.
Even though Gaza has experienced some economic growth in recent years, the report says it "does not seem to be sustainable" and finds that Gazans are worse off now than in the 1990s.
Unemployment was at 29% in 2011 and has risen since then, particularly affecting women and young people.
Traffic through the cross-border tunnels was hit in recent weeks by violence between Egyptian security forces and militants in Egypt's Sinai peninsula, which borders Israel and Gaza.