Didier Trebucq said nearby islands including Barbados, Antigua and Barbuda could also be badly affected. He said the UN was setting up an international funding appeal.
About 20,000 people have been evacuated from their homes since La Soufrière volcano began erupting last Friday. It had not previously erupted since 1979.
Mr Trebucq, the UN co-ordinator for Barbados and the Eastern Caribbean, said clouds of ash and smoke were continuing to pour from the volcano every day.
“This is a crisis that is going to last certainly more than six months in the sub-region, in Saint Vincent, and other islands,” he said. The UN says about 4,000 of those displaced are now living in 87 shelters – many of which lack basic services such as drinking water. Others have moved in with family or friends and some have taken boats to neighbouring islands.
Mr Trebucq said water provision was the main priority for aid teams, followed by shelter. “The clean-up of the ashes, finally, is another important priority, in terms of environmental health but also clean-up to make sure that life can come back to normal outside the red zone as soon as possible,” he added.
On Wednesday, Prime Minister Ralph Gonsalves said that despite the dangers many residents were choosing to stay on the island rather than be evacuated by ship.
“There are some people who want to go to different countries but it is not a large number,” he told a TV programme in Grenada.
“They said they want to stay at home. I have been around several of the camps and that’s the message.”
(Al Jazeera Pic)