A strong magnitude 6.5 earthquake has struck Papua New Guinea, authorities say, but there was no tsunami alert or immediate reports of damage.

The quake struck the South Pacific Island nation 110km southeast of the West New Britain provincial capital Kimbe at a depth of 68km shortly before 7am on Monday, the US Geological Survey said in a statement.

The US Tsunami Warning System said there was no tsunami alert.

Papua New Guinea sits on the Pacific "Ring of Fire," the arc of seismic faults around the Pacific Ocean where much of the world's earthquake and volcanic activity occurs.

Australian Associated Press