The population has dropped by about 160,000 since Israel began its offensive on Gaza, the Palestinian Authority for Statistics said.
Gaza's population has fallen by 6 percent since Israel launched an attack on the encircled Palestinian enclave nearly 15 months ago, according to the Palestinian Observatory.
About 100,000 Palestinians have left their homes while more than 55,000 are thought to have lost their lives, the Palestinian Central Bureau of Statistics (PCBS) said in a release on Tuesday.
About 45,500 Palestinians, more than half of them women and children, have been killed since the war began and another 11,000 are missing, the office said, citing figures from the Palestinian Ministry of Health.
Accordingly, Gaza's population has dropped by about 160,000 during the war to 2.1 million, and more than a million, or 47 percent of the remaining population, are children under the age of 18, PCBS said.
It said Israel “has carried out barbaric attacks against Gaza against all kinds of life there; people, houses and infrastructure… all families were erased from the civil register. There are dangers that destroy people and property.”
Israel's Foreign Ministry said the PCBS information was “created, inflated, and manipulated to defame Israel”.
Leading rights groups have criticized Israel for its brutality in its war in Gaza, citing the high level of death and destruction and the refusal to provide essential services, including humanitarian aid.
The International Court of Justice (ICJ), the highest legal body of the United Nations, ruled last January that Israel must stop the killing of Palestinians, while Pope Francis of the Roman Catholic Church said that people around the world should learn from Israel's campaign to Gaza is killing people.
Israel has repeatedly denied the accusations, saying it abides by international law and has the right to defend itself against Hamas.
The Israeli army has continued to close key border crossings into Gaza, preventing the entry of much-needed aid, including food and medicine.
In the northern part of the Strip, a widening siege has been imposed since the Israeli army launched another offensive there in October. Residents there are trapped, facing an impending famine, and enduring Israeli bombardment as major hospitals have been attacked and burned.
PCBS said that approximately 22 percent of Gaza's population is currently facing severe food insecurity, according to the Integrated Food Security Phase Classification, an international monitoring system.
Included in the 22 percent are 3,500 children who are at risk of dying from malnutrition and lack of food, the agency said.
About 60,000 pregnant women also face serious health risks in Gaza, the report said, due to the deterioration of the health sector and the lack of medical care.
Children are often born in difficult circumstances, and families are unable to provide adequate support such as medical care.
Several babies have they lost their lives in recent days without access to hospitals and because of the intense heat, the press office of the Gaza government said.
Israel's war has displaced almost all of Gaza's population, forcing tens of thousands of people inside temporary tents in open camps.