[Updated at 6:27 a.m.] Vanessa del Leon, who works at a hotel in David, said she felt the quake, whose epicenter was 110 miles south of the city.
"Everyone started screaming. We heard a lot of things breaking and computer keyboards smashing on the floor," she said. "This hotel has eight floors and it swayed like a palm tree."
The USGS had said the quake was a magnitude 6.1, but later revised it to 6.0. It hit at 3:19 a.m. local time, according to the USGS.
[Posted at 5:43 a.m.] A 6.1-magnitude earthquake struck southern Panama on Saturday, the U.S. Geological Survey said.
The quake hit 384 kilometers (238 miles) southwest of the capital, Panama City.
There were no immediate reports of damage.