A powerful undersea earthquake shook Papua New Guinea early Monday, the U.S. Geological Survey said. There were no immediate indications of whether it caused damage, injuries or a tsunami.

The quake had an initial magnitude of 6.8 and struck at 12:20 a.m. in the New Britain region of Papua New Guinea, the USGS said.

Its center was estimated to have been at a depth of six miles, it said.

The region is about 1,440 miles north of Brisbane, Australia.