SYDNEY (Reuters) - A magnitude 5.4 earthquake struck on Monday about 83 kms (51.57 miles) southwest of the town of Isangel in the South Pacific Island nation of Vanuatu, the United States Geological Survey said.

The temblor was initially reported to have been a much more powerful magnitude 6.3, but the USGS revised down its initial assessment.

(Reporting by Matt Siegel; Editing by Michael Perry)