Vanuatu authorities are warning people to stay off Mount Yasur volcano on Tanna island.
The mountain is one of the most accessible volcanos in the world and it's a favourite spot for tourists.
The general manager of the department of geology and mines, Esline Garae, says seismic monitors have measured a surge in activity over the last two weeks.
"The volcanic seismicity, recorded at the proximity of Yasur, shows an increase of activity since mid-September 2005, and this could be the warning signs of high explosive activity."
Ms Garae says ash from eruptions on Mount Yasur usually doesn't fall near settlements.
The Vanuatu Tourism Office is urging visitors to respect Ms Garae's advice.