A powerful earthquake rattled the South Pacific island nation of Papua New Guinea on Friday, but no tsunami was seen and there were no immediate reports of damage or injuries.

The 6.8-magnitude quake struck about 66 miles southwest of the town of Kokopo in northeastern Papua New Guinea, the U.S. Geological Survey reported. It also said the quake's strength was lower than the initial measurement of 7.1.

The Pacific Tsunami Warning Center said hazardous tsunami waves were possible within 186 miles of the epicenter, but the risk passed shortly thereafter and the advisory was lifted.

There were no reports of damage or injuries, said Chris McKee, assistant director Geophysical Obervatory in the capital, Port Moresby. The area closest to the epicenter is sparsely populated, and it was unlikely the quake caused any structural damage, he said.

There were also no reports of any tsunami sightings. Given the quake's depth of about 37 miles, officials believed the risk of a tsunami was slim, said observatory official Mathew Moihoi. Shallower quakes tend to cause more damage, and have a higher potential for generating a tsunami.

Papua New Guinea sits on the Ring of Fire, the arc of seismic faults around the Pacific Ocean where earthquakes are common.