Sydney: An earthquake of magnitude 7.3 struck off the coast of Vanuatu on Monday, the United States Geological Survey (USGS) reported.

The quake hit around 35 kilometres (22 miles) northeast of Luganville, the Pacific island nation's second-largest city, according to the USGS, which revised up the magnitude from an initial 7.2.

There was no threat of a tsunami, according to the Pacific Tsunami Warning Centre.

Earthquakes can occur anywhere between the Earth's surface and about 700 kilometres below the surface. For scientific purposes, this earthquake depth range of 0 - 700 km is divided into three zones: shallow, intermediate, and deep, as per USGS data.

Shallow earthquakes are between 0 and 70 km deep; intermediate earthquakes, 70 - 300 km deep; and deep earthquakes, 300 - 700 km deep. In general, the term "deep-focus earthquakes" is applied to earthquakes deeper than 70 km, the USGS states.