According to The Associated Press, the earthquake caused "small landslides," damaged homes and knocked out power in some areas.
The second earthquake, which was reported around 10:51 a.m., struck about 4 miles south of Tallaboa, according to USGS officials.
Earthquakes between 4.7 and 5.1 magnitudes have shaken the southern region of Puerto Rico several times Dec. 28, according to the AP.
"This is one of the strongest quakes to date since it started shaking on Dec. 28," Angel Vazquez, emergency management director for the city of Ponce, told the AP. "It lasted a long time."
In a pair of tweets, Gov. Wanda Vázquez Garced said she was in "direct communication" with mayors of Guayanilla and Guánica, as well as other officials.
"Citizens must remain calm and have their action plans prepared to protect themselves," she tweeted.
Read more here.