It said the quake struck the center of the island, Vanuatu's fourth largest, at 7:09 a.m. (2009 GMT on Wednesday) and was fairly deep at 124.4 miles (200 km), which would have dampened its effect.
Erromango has a population of just under 2,000 people.
The Vanuatu archipelago, east of Australia in the Pacific Ocean, is in the so-called Ring of Fire and is prone to earthquakes.