Dahshur, one of the oldest burial grounds in Egypt, is full of holes made by grave robbers, guards said.
"We wanted to catch them," a guard said in a report by Germany's Der Spiegel Wednesday. "But they opened fire on us with automatic weapons."
Guards, who only had pistols, jumped for cover and the robbers carried on with their plundering.
Archaeologists partially mapped out the Dahshur site but never exhumed its contents, making it a big draw for thieves.
At the pyramids of Saqqara, grave robbers cleared out a state-owned storehouse containing small statues.
Reports indicate there have been illegal excavations in the tourist centers of Aswan and Luxor where organized gangs used small excavators instead of shovels.
Since the Egyptian revolution in 2011, grave robbing has been on the increase, said Abdel-Halim Nur el-Din, archaeology professor and former head of the Supreme Council of Antiquities.
"We are losing our cultural heritage piece by piece," he said.