The United States Geological Survey says an undersea volcano near Farallon de Pajaros in the Northern Marianas can erupt any time.
The agency's Hawaiian Volcano Observatory has been keeping a close eye on the undersea volcano that has been showing signs of activity in recent days.
According to a weekly summary issued by the Observatory, recent seismic activity almost certainly herald an eruption.
According to the USGS report, seismometers on the islands recorded high levels of seismicity and the most likely source of the volcanic activity is the Ahyi seamount, which is about 20 kilometres southeast of Farallon de Pajaros.
The seamount rises to within 64 metres of the ocean surface and is associated with several reports of possible eruptions in historical times, the most recent in 2001.