The site was discovered in January during preparations for an Egyptian-funded housing project, the organisation said.
Work crews have been excavating the site since the discovery at the start of the year.
A total of 63 graves have been identified, with a set of bones and artefacts from one tomb was dated back to the second century, said Hiyam Al Bitar, a researcher from the Hamas-run Ministry of Antiquities and Tourism.
The ministry is working with a team of French experts to learn more about the site, she said.
On Sunday, workers sifted through the soil and removed piles of dirt in wheelbarrows.
Although the ancient cemetery is now blocked off from the public, construction on the housing project has continued and the site is surrounded by apartment buildings.
Media reported looting when the site was first discovered, with people using donkey-drawn carts to haul away items like a covered casket and inscribed bricks.
Gaza, a coastal enclave home to more than two million people, is known for its rich history stemming from its location on ancient trade routes between Egypt and the Levant.
But Israeli occupation, a blockade, conflicts and rapid urban growth in the crowded, narrow territory are among the reasons most of Gaza’s archeological treasures have not been protected.