The entire 11,000 population of Ambae, in the north of the Pacific archipelago, was ordered to leave last week after the Manaro Voui volcano rumbled to life and rained rock and ash on villages.
New Zealand volcanologist Brad Scott is in Vanuatu and flew over the Ambae volcano on Monday - one of three active in the area.
He observed a small lava flow, up to 80 metres long, pouring into the lake surrounding the summit.
While the level of activity has stabilised, it has not decreased either.
"The eruption is not escalating and growing any more. The local government has taken a precautionary measure for public safety. How long the evacuation will last, unfortunately there is no way to tell," Mr Scott said.
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Evacuation ahead of schedule
The evacuation to nearby islands was scheduled for completion by this Friday but the Red Cross said it was likely to wrap up on Wednesday.
It said villagers were exiting the island on a range of locally-commissioned boats - from barges carrying hundreds of people to smaller ferries shipping dozens at a time.
"You have got a huge range of boats that are transferring 11,000 people from Ambae to the three surrounding islands. For a country this size it is a very big operation," Red Cross spokesman Joe Cropp said.
"It was orderly. People realised that they need to leave, there is a lot of patience among the community."
Most of the island's residents have been sheltering in evacuation centres since the volcano first sent up a plume of steam and ash about a week ago.
They are leaving from three coastal locations and the point on Ambae's western edge had already completed its evacuation on Monday.
The Red Cross is delivering water to the island after ash from the volcano contaminated fresh supplies.
While an orderly evacuation was still a priority for those remaining, attention was now turning to the strained resources at the islands to which people were being relocated, Cropp said.
The relocation facilities on surrounding islands are "starting to handle" the situation, "but we need to step up quickly, we need to get the resources in to provide the shelter, water, food and sanitation that people need," he added.
An Australian naval ship is expected to arrive on Wednesday, while New Zealand has sent a Hercules C-130 to airlift supplies into the area.
Vanuatu lies on the Pacific "Ring of Fire" where tectonic plates collide, causing frequent seismic and volcanic activity.
