Operations Manager of the NDMO Peter Korisa said about 1000 people of the island's 10,000 inhabitants had already left of their own accord.
He said the island's volcano had been erupting since last September but increased its activity in April with ash fall ruining crops and volcanic gases contributing to acid rain contaminating water supplies.
He said the volcano was unpredictable and the government is advising people to take up the government's help to leave if they are not coping but he predicted most were likely to stay.
"We are still yet to confirm the number but we are looking at not quite a big number, it's just a thousand-plus. If we are to move people like people in the evacuation centres right now, that's our priority one to move those people.
"Because they've already moved out from their homes and they are in evacuation centres. So it's about a thousand-plus, or it's not really a big number."
Peter Korisa said the government is planning for the evacuation to start in June with most people going to the nearby island of Maewo which currently has a population of about 3500.