A state of emergency has been declared on Ambae in the South Pacific island nation of Vanuatu after a volcanic eruption forced half of the island's population to be evacuated to nearby villages, the Deutsche Presse-Agentur, DPA, has reported.

Authorities are preparing for the eruption to get worse, with the possibility of the entire island being evacuated, Radio New Zealand reported on Tuesday.

The volcano, known as Monaro, at the island's centre, has been rumbling for weeks, but its activity has increased rapidly since the weekend, with eruptions and ashes covering much of Ambae.

Some 5,000 villagers from the island's north and south have been evacuated by Vanuatu's Disaster Management Committee to camps in the east and west.

The country's geohazards department issued a 'level four' alert that could be upgraded.

At the moment, the volcano has blown up ash and dark smoke, with a little bit of lava, according to Manuel Amu, the chairman of the Disaster Management Committee, who was talking to Radio New Zealand.

"Moving people from their communities into an area with very limited houses and very limited resources like food and water [is] really a challenging issue," he said.

According to Radio New Zealand, there is growing fear among those being evacuated as shelter has started to run out and locals have reported louder eruptions.

Amu said the villages are facing major hazards like ash fall and acid rain, as well as the possibility of rocks and volcanic fragments being hurled through the air by eruption activity.

Amu said that up to 3,000 more people are expected to arrive at the temporary shelters, while others have already left the island, added DPA.