The 6.0 aftershock happened eight miles away from Guanica around 9 a.m., according to the National Weather Service.
Back to back aftershocks hit the island on Monday and Tuesday close to the town of Tallaboa and in the city of Ponce that left one person dead. Several citizens were injured, several buildings including schools and a popular tourist landmark were destroyed.
A tsunami warning was not issued as the aftershocks were not strong enough to cause one, Dr. Lucy Jones, a seismologist told ABC News.
Over 4,000 people are living in shelters and and thousands of customers were without potable water. "An additional 3,500 people are in non-traditional sheltering due to concerns about aftershocks," FEMA said in a press release issued on Saturday.
Puerto Rico Electric Power Authority (PREPA) said that some municipalities in the south of the island have lost power because of the latest quake.
Before the Saturday shaker, PREPA restored power to about 65% of its customers.
FEMA said they expect 100% power restored on Sunday, but "there will be little to no reserve capacity."