The quake, centered about 3 miles south-southwest of Tallaboa, occurred at 4:24 a.m. local time, according to the U.S. Geological Survey. The temblor did not pose a tsunami risk, officials with the National Weather Service said in a Twitter post.
Several subsequent quakes followed, ranging from 3.7 to 5.6 in magnitude, the USGS reported.
President Donald Trump signed an emergency declaration for Puerto Rico on Tuesday night, the Federal Emergency Management Agency said in a statement.
"Specifically, FEMA is authorized to identify, mobilize, and provide at its discretion, equipment and resources necessary to alleviate the impacts of the emergency," the statement read.
Rey Gonzalez told The Associated Press that his uncle was killed when a wall collapsed on him at the home they shared in the city of Ponce. He said 73-year-old Nelson Martínez was disabled and that he and his father cared for him.
Eight people were injured in Ponce, near the epicenter of the quake, Mayor Mayita Meléndez told WAPA television.
Officials with the Electric Power Authority, PREPA, said in a statement Tuesday that damage was reported at a power plant in southwestern Puerto Rico, knocking out power to nearly the entire island, according to USA Today. Barring any additional major damage, power was expected to be returned to the island later Tuesday, PREPA CEO Jose Ortiz said.
“We are evaluating substations throughout the island,” Ortiz said. "If no other (major) issues occur with our system we should reenergize early during the day.
Tuesday morning's earthquake was the latest in a string of temblors reported on the island in recent days, according to Reuters. A 5.8 magnitude earthquake and a subsequent 5.1 magnitude aftershock struck the U.S. territory Monday, causing "small landslides," damaging homes and knocking out power in some areas, according to the AP.
They earthquakes were reported as Puerto Ricans continued to recover from a pair of hurricanes that swept over the island in 2017, killing about 3,000 people and severely damaging the island's infrastructure, Reuters reported.
The Associated Press contributed to this report.
Check back for updates to this developing story.