A volcanic eruption in New Zealand killed at least five people and left many more presumed dead Monday on a small volcanic island off the country's northeast coast.

Police said White Island, also called Whakaari, is still too dangerous for search and rescue crews but that multiple reconnaissance aircrafts have flown over since the eruption Monday afternoon and "no signs of life have been seen at any point."

Fewer than 50 people were on the island when it erupted, and 23, including the five confirmed dead, have been evacuated, said Police Deputy Commissioner John Tims.

"Anyone who could have been taken from the island alive was rescued at the time of the evacuation," police said in a news release.

Prime Minister Jacinda Ardern called the eruption "very significant" and traveled to the area Monday. "All our thoughts are with those affected," she said.

Here's what we know now:

What happened on White Island?

According to GeoNet, which tracks volcanic activity in New Zealand, the eruption occurred just after 2 p.m. local time.

The eruption was "short-lived" and sent an ash plume soaring about 12,000 feet above the volcano's vent, according to GeoNet volcanologist Geoff Kilgour.

Both New Zealanders and tourists were among the dead, missing or injured, said Tims. Many of the 18 survivors were injured, some with severe burns, he said.

Police said they were working to confirm the exact number of deceased but "do not believe there are any survivors on the island."

Videos and photos shared on social media show massive plumes of smoke coming off the island.

A Royal Caribbean International cruise ship, Ovation of the Seas, was on the island at the time, the company confirmed. The ship was to sail to Wellington on Monday, but instead would remain in the Tauranga port overnight to learn more, the company said.

Australian Prime Minister Scott Morrison said 24 Australians were on the island as part of a cruise ship tour. There were still people, including Australians, unaccounted for, he said.

Kilgour wrote that volcanic activity on the island has since diminished. Volcanic activity on the island reached an alert level of four out of five immediately following the eruption but has since been lowered to three, indicating a "minor local eruption is in progress."

“In the scheme of things, for volcanic eruptions, it is not large,” said GeoNet's Ken Gledhill. “But if you were close to that, it is not good.”

Where is White Island?

White Island is about 30 miles off New Zealand's North Island in the Bay of Plenty. It is also known by its indigenous Maori name Whakaari.

The cone volcano is New Zealand's most active, experts say, and about 70% of it sits under the sea.

According to the New Zealand Herald, a shelter was installed in 2016 on the island in case of unexpected eruptions.

The island has a history of mining but is now a tourist attraction. The island became a private scenic reserve in 1953, and more than 10,000 people visit the volcano each year on daily tours.

Were there warning signs that the White Island volcano would erupt

GeoNet had raised its alert level on the island from one to two on Nov. 18 as sulfur dioxide gas increased.

According to GeoNet, a level two warning is means there are "unrest hazards on the volcano and could include eruptions of steam, gas, mud and rocks. These eruptions can occur with little or no warning."

GeoNet had been providing updates on the volcanic unrest on the island in the days leading up to the eruption.

"Volcanic gas emission and seismic activity continue to remain elevated," GeoNet's Brad Scott wrote last Tuesday. "Observations and data to date suggest that the volcano may be entering a period where eruptive activity is more likely than normal."

Scott said alert levels can often raise then fall without an eruption.

What's next for search and rescue crews?

A naval ship plans to approach the perimeter of the island early Tuesday and will deploy drones and other observational equipment, police said.

A disaster identification team was forming at Whakatane, a city south of White Island on North Island.

Prime Minister Ardern said rescue efforts remained the focus remained and questions over whether tourists should be visiting would be addressed later.