Sydney -- A strong earthquake with a preliminary magnitude of 6.3 has struck off the Papua New Guinea island of Bougainville early on Tuesday morning.

The earthquake, at 2:19 am Tuesday local time, was centered about 94 kilometers southwest of the town of Panguna on Bougainville Island, which sits to the northwest of the Solomon Islands. It struck about 30 kilometers deep, making it a shallow earthquake.

The Pacific Tsunami Warning Center initially measured the earthquake at 6.7 before it was downgraded to 6.3 by the United States Geological Survey (USGS).