The European-Mediterranean Seismological Centre and the U.S. Geological Survey said the quake struck at 1343 GMT (9:43 a.m. EDT), followed by a 5.2-magnitude temblor eight minutes later.
The USGC said the stronger quake hit at a depth of 5.3 miles (8.6 kilometers), 58 miles (93 kilometers) northwest of Jan Mayen, a Norwegian island with a research station but no permanent population.
The quake could be felt on the island, but didn't cause any damage or injuries, said Erik Persheim, an electronics engineer at the research station.
"We watched the mountain as the loose stones and shale came sliding down," Persheim told The Associated Press. "It didn't seem very big and I don't think much of anything broke, but we'll have to have a thorough inspection."
He said there are currently 44 people on island involved in various research and maintenance work. Normally, the station houses about 18 engineers and other personnel.
Norwegian seismologist Tormod Kvaerna said Jan Mayen, about 370 miles (600 kilometers) east of Greenland, lies near a fault line and is often exposed to earthquakes though he couldn't remember any previous temblors there of that size.
"This is very big," he said, adding that it probably wasn't
In 2008, a 6.2-magnitude earthquake off the Svalbard islands was billed as the most powerful earthquake on record in Norway.
It was unclear whether the epicenter of Thursday's quake was inside Norwegian territorial waters.