There were no immediate reports of damage.
The quake’s epicentre was off the Romanian and Bulgarian Black Sea coasts, and its estimated depth was 10 km (6 miles).
“It was a very short tremor which occured at 0749 GMT … the epicentre was next to the Romanian/Bulgarian coasts,” an official from the institute said.
(Reporting by Radu Marinas; Editing by Kevin Liffey)