The buffer, which will include observation towers, cameras and lighting, will be 100 feet wide and 7.5 miles along the southern border of the strip's coast and the Sinai Peninsula, the Hamas interior ministry said.
The construction of the buffer zone "is a reassuring message directed at the Egyptian side that the national security of Egypt is the national security of Gaza," Tawfiq Abu Naim, a security chief of the Gaza-based group, said in the statement.
"These continuing measures are for the sake of achieving control of the southern border and to completely prevent infiltration and smuggling," he added. "We can not allow any threat to the stable security situation on the southern border."
He said the project was agreed upon during a nine-day visit to Egypt by a high-level Hamas delegation to Egypt earlier this month.
Hamas is seeking to improve relations with Egypt since the overthrow of Mohamed Morsi, Egypt's Muslim Brotherhood president, in 2013. Hamas was affiliated with the Brotherhood.
In exchange for Hamas agreeing to security demands and handing over 17 men wanted by Cairo on terrorism charges, Egypt offered more freedom at its border and electricity amid a severe power shortage, according to London-based Arabic daily Asharq al-Awsat. Israel began reducing electricity to the Gaza Strip last week, fulfilling a request from the Palestinian Authority to pressure Hamas from controlling the region.
Last month, Hamas approved a new policy document that dropped its longtime association with the Muslim Brotherhood, dropped its longstanding call for Israel's destruction and instead would accept the formation of a Palestinian state along the 1967 borders in the West Bank and Gaza Strip.
Cairo has closed most of the border between Egypt and Gaza.
The current Egyptian government, under former military leader Abdel Fattah al-Sisi, also has closed smuggling tunnels along the border and accused Hamas of supporting Islamist radicals inside Egypt.
Hamas will have to pay families compensation or find them alternative housing affected by the buffer, Sources in Gaza told Haaretz.