One of the aftershocks was nearly as powerful as Thursday's earthquake, which brought a school down onto an entire class of 6-year-olds and their two teachers.
More than 30 people were pulled alive from the rubble of other buildings in the medieval village, but rescuers have concluded that none survived in the school.
Friday's tremors in the remote Molise region measured 3.4 to 5.3 on the Richter scale and occurred over the course of the afternoon, local time.
No deaths had been reported by evening, but authorities have ordered schools closed in the area and told residents they must leave their homes.
Many of San Giuliano's 1,500 villagers have moved to blue tents set up on the surrounding plains, and emergency supplies are pouring in.
Across the region, about 3,000 people have fled their homes, according to the Italian news agency, ANSA.
Dozens of buildings and homes in the area collapsed or were severely damaged in Thursday's quake. Phone lines in the area were down, and authorities closed several bridges thought to be at risk for structural damage as a result of the earthquake.
Authorities said that the powerful quake on Thursday measured 5.4 on the Richter scale and was centered just outside the regional capital, Campobasso, around 140 miles southeast of Rome.
The Italian National Earthquake Center in Rome said that the earthquake was the strongest to hit Italy since a 5.8-magnitude quake hit just north of Rome in 1997.
It is the strongest on record for the area around Campobasso.
"This is not an area especially known for earthquakes, but it is surrounded by areas where earthquakes are more common," a spokesman for the center told United Press International.
"One problem with this situation is that the area is quite remote and access and infrastructure is somewhat limited."
The problem was further complicated by the fact that dozens of expert rescue workers from the area had been sent to Sicily to help residents in the wake of a series of smaller earthquakes and the eruption of Mount Etna, Europe's largest volcano.
According to TV reports, tremors were felt as far away as Rome to the northwest, Naples to the west and Bari to the southeast.