WELLINGTON, Dec. 9 (Xinhua) -- A volcano erupted at New Zealand's White Island on Monday about 2:11 p.m. local time (0111 GMT), according to GeoNet, the country's geological hazard information center.

"We are aware that people were on the island immediately before the eruption and we express our concern for their safety," the agency said on its website.

It said the "short-lived" eruption generated an ash plume of over 3,000 meters above the vent, adding the ash fall appeared to be confined to the island.

"We have seen a steady decline in activity since the eruption," it added.

The agency put the Volcanic Alert Level to Level 3, with the Aviation Color Code remained at Orange.

Media reports quoted New Zealand Prime Minister Jacinda Ardern as saying that around 100 people were on or around the island at the time of the eruption, and some of those are "unaccounted for."

"A number of people are reportedly injured and are being transported to shore," she was quoted as saying.