The Vanuatu Meteorology and Geohazards Department is warning tourists and aviation centres of the drastic change in activity.
Meteorologist Esline Bule said the background noise and gas levels on Ambryn were very significant and while ash has settled a little on Ambae, seismic activity remains at level three, indicating minor eruptions.
"Already Ambae there's a significant ash fall last weekend, in the western part. Ambryn, the volcanic ash is not manifested much yet in the villages. But there's things happening at the top in the crater."
Esline Bule said tourists were currently under some restrictions and must stay at least at least three kilometres away from the craters of both islands.
RNZI reports Mt Yasur, on the island of Tanna, is also having minor eruptions and is known for being unstable so it is currently classified as level 2 indicating major unrest.
She said the service was also reviewing new data from the island of Lopevi and will notify the Volcanic Ash Advisory Centre in Wellington if the alert level is increased, and new flight diversions are necessary.