Authorities say the suspects started their heist from an empty building adjoining Milano's Fine Jewelry, then cut through a concrete wall.
Police say it must have taken hours for the suspects to get into the store, then into its safe. The crime was discovered Monday morning.
Forsyth County sheriff's Capt. Tim House tells WSB-TV that it's one of the largest such crimes he's seen in his 25 years of experience.
Store owner Ibrahim Ehicam says the thieves emptied all the display cases and even stole the cash register.