Lava began oozing out of La Soufrière volcano in St. Vincent and the Grenadines on Dec. 29.
Scientists with the Seismic Research Center at the University of the West Indies said there was no explosive eruption. Instead, the magma reaching the surface is forming a growing dome in La Soufrière's crater. The volcano is also releasing gas and steam.
The alert level on the northern end of the island of St. Vincent, where La Soufrière sits, has been raised to orange, which means an eruption could occur with less than 24 hours' notice.
However, no evacuations have been ordered, according to the country's National Emergency Management Organization.
People living near the volcano could experience strong sulfur smells for several days or weeks, the Seismic Research Center said.
The last time La Soufrière erupted in 1979, more than 20,000 people were evacuated. An eruption in 1902 killed 1,565 people. Before that, the last major eruption was in 1812.
About 100 miles to the north, Mt. Pelée on the French island of Martinique also is rumbling.
On Dec. 3, officials with the Martinique volcanological and seismological observatory advised raising the alert level to yellow after detecting seismic activity under the mountain, according to a news release from the observatory.
An increase in seismic activity since April 2019 and the detection of two tremors on Nov. 8 and 9 led the observatory to recommend raising the alert level, which the government did.