About 3500 evacuees arrived on the island of Espiritu Santo overnight, bringing the total number of evacuees close to 5000, with up to 4000 more still to leave Ambae.
Provincial officials said the 19 evacuation centres on Santo were already filled to capacity and about 1000 evacuees have yet to be processed.
The government wants the entire population evacuated by Friday, but officials said the original figure of 11,000 given for Ambae's total population could be too low.
The dramatic increase in arrivals in Santo was also being put down too many evacuees refusing to go to other islands like Maewo and Pentecost.
An official, Jacques Tronquet, said they had the ground space to accommodate more refugees but they needed about 1000 more large tents.
Mr Tronquet said the hardest thing, from a planning perspective, was no one knows what the volcano is going to do.
He said they currently had enough food staples to last a week, but if it goes on much longer they will need more government funding.
Threat level remains high
The threat level of the volcano remains at four, one step away from a full-blown eruption.
"What we're telling everybody now is life is paramount and properties are secondary," Vanuatu police commissioner Albert Nalpin said.
Most people are going to Santo, which expects to receive more than 7000 evacuees by the end of the week.
But the government-sanctioned evacuation has been slow to come. Santo resident Andrew Ala said locals have taken the initiative to look after people who have been fleeing the volcano.
"Everyone comes here as a transit point. We give them some food and then ... the disaster committee takes them to the evacuation centres."
RNZ Pacific reporter Koroi Hawkins told Morning Report he has been out on the water and seen the boats picking people up.
He said the island of Santos has a population of about 40,000 so the number of people coming off Ambae was stretching resources.
Loren Urinmal, president of the nearby Malampa province, where about 2000 evacuees are being hosted, said some community members have even been asking to adopt families and give them land to live on.
But most evacuees spoken to by RNZ Pacific said they intend to return home as soon as it is safe to do so.
Speaking in Bislama, Marilyn Tari said it was very hard leaving her home.
"So many of us cried when we heard how bad it was and we thought of our home - how important it is [to us].
"And so when we left our home and travelled here, it is really difficult to come and try and live here in a new place."
Kiwi aids evacuation efforts
A young New Zealand pilot helping to evacuate people from an erupting volcano in Vanuatu said he had been both deeply moved and humbled by the experience.
Most of Ambae's population is leaving by boat, but the sick, the elderly and people with disabilities are being flown out on chartered flights.
Adam Reid, 22, who is originally from Auckland, has racked up about 35 such flights over the last three days, helping move about 300 people off Ambae.
Mr Reid said when he landed the job with Air Taxis Vanuatu 18 months ago, he never thought he would be involved in helping people escape an erupting volcano.
"It took a bit of an impact on me, seeing that... But it's just a good thing to be able to help."
Photo: RNZ Ambae Island volcano