Kick 'em Jenny - the oddly named underwater volcano about five miles off the coast of Grenada in the Caribbean sea - could erupt soon, say researchers.
The eruption could destroy ships within the vicinity, sinking them without trace.
The volcano - which sits 180m below sea level - has produced no less than 200 small earthquakes since it began stirring on July 11.
Experts at the University of the West Indies' Seismic Research Centre have now raised its threat level to orange, predicting that it could erupt at any point.
If it were to, then both passing ships and nearby islands will be in danger of being hit by a tsunami, reports the Daily Mail.
Scientists say the risk is relatively low, but both shipping and marine vessels in the region have been urged to take heed, with recreational ships ordered to stay at least 3 miles from the summit.
Volcano killed 60 people in 1944
Submarine volcanoes are known to release intense amounts of gas bubbles before they erupt, in a process known as degassing. These bubbles lower water density, thus causing ships to lose buoyancy and sink.
Any eruption could also see Kick 'em Jenny spout hot rocks out of the water and three miles into the air. They also pose a significant risk to ships caught in the vicinity.
In 1944, degassing from Kick 'em Jenny caused a passenger vessel to sink, killing 60 people. Its last eruption was in 14 years ago, in 2001.
The volcano rises 1,300m above the sea floor on the steep inner western slope of the Lesser Antilles ridge.