Vanuatu's East Epi underwater volcano erupted on Wednesday, hurtling ash into the sky and leading authorities to warn ships and aircraft to avoid the area.
"We are telling locals to watch out for any strong explosions as the eruptions are still ongoing," senior volcano officer Ricardo William, at the meteorology and geo-hazards department, told AFP.
A 10-kilometre (6.2-mile) "danger zone" has been established around the submerged volcano, which lies 68 kilometres north of the capital Port Vila.
After reports of steam over the site, the underwater volcano started belching ash up to 100 metres high early Wednesday.
Volcanic activity started shortly before 8 am (2100 GMT Tuesday), according to the local meteorology department.
Eyewitness Philip Dick, a government official, told AFP the ground started shaking and smoke above the site was visible in the early hours.
"Then the explosions began -- there is still a bad smell of sulphur within the nearby villages," he added.
Officials raised the volcano alert to the first level, meaning "minor unrest", on a scale of one to five.
Locals on the nearby islands of Epi and Tongoa have been told to avoid the coast.
"People are advised to stay on alert... the ongoing volcanic eruptions could trigger a possible tsunami," the department said in a statement.
It added that, while the Alaska-based Tsunami Warning Center had not picked up any activity in the Vanuatu region, "such eruptions have the potential to create tsunami waves".
The Pacific island nation was rocked by a 7.0-magnitude earthquake in early January off the largest island Espiritu Santo in the north of the archipelago.
Vanuatu is in the Pacific "Ring of Fire", where tectonic plates collide.
It experiences frequent seismic and volcanic activity.
