"Things are escalating pretty quickly," she said of the volcanic activity, adding that it was impossible to provide an exact forecast of what might happen in the next hours or days.
The volcano last erupted in 1979, and a previous eruption in 1902 killed some 1,600 people.
The eastern Caribbean is home to other active volcanoes. Seventeen of the region's 19 live volcanoes are located on 11 islands, with the remaining two underwater near the island of Grenada, including one called Kick 'Em Jenny that has been active in recent years.
The region's most active volcano in recent years has been Soufriere Hills in Montserrat, which has erupted continuously since 1995, destroying the capital of Plymouth and killing at least 19 people in 1997.