SYDNEY (AFP) - A strong, 6.4-magnitude earthquake struck deep off the coast of Papua New Guinea Wednesday, the US Geological Survey said. No Pacific Ocean tsunami or damage was expected.

The quake hit at 5:15 pm (0715 GMT), 110 kilometres (69 miles) southeast of Madang, a province on the northern coast of mainland PNG, the USGS said.

It struck at a depth of 213 kilometres, and seismologists said it was unlikely to trigger a tsunami or cause any damage, with Geoscience Australia estimating its danger radius at 54 kilometres from the epicentre.

Papua New Guinea, which is mired in poverty despite rich mineral deposits, sits on the so-called "Pacific Ring of Fire", a hotspot for seismic activity due to friction between tectonic plates.

It was rattled by a series of quakes measuring between 6.9 and 7.3 magnitude last month but no damage or tsunami was reported.