More than 20 Australians, including a newlywed couple from Brisbane, are among those still missing after the White Island volcano eruption on Monday.

The New Zealand Red Cross Family Links website went down on Tuesday morning as desperate family members waited for updates on loved ones following the devastating explosion in New Zealand's Bay of Plenty.

Overnight, around 25 Australians were listed by family members as missing.

Speaking to reporters on Tuesday, Prime Minister Scott Morrison put the number at 24 but said 13 of those were in hospitals, with 11 still unaccounted for.

New Zealand authorities have so far confirmed five people are deceased.

"We fear of the five deceased persons, that three of those, up to three are Australians, but that is not yet confirmed," Mr Morrison told reporters.

Here are the Australians listed as missing on the Red Cross website:

• Amy Miall, 30, of Brisbane

• Anthony Langford, 51, of North Sydney

• Gary Woolley, of Sydney

• Gavin Brian Dallow, 53, of Adelaide

• James Whitehouse, 23, of Brisbane

• Jane Murray, 56, of Sydney

• Jason David Griffiths, 33, of Coffs Harbour NSW

• Jesse Langford, 19, of North Sydney

• Jessica Richards, 20, of Australia

• Julie Richards, 47, of Australia

• Karla Michelle Mathews, 32, of Coffs Harbour NSW

• Kristine Langford, of Australia

• Lisa, 48, of Adelaide

• Madeleine Whitehouse, 24, of Brisbane

• Marion London, 56, of Sydney

• Martin Hollander, 48, of Australia

• Mathew Thomas, 31, of Tamworth NSW

• Maureen Jones, 68, of Bathurst NSW

• Mitchell James O'Shea, of Canberra

• Richard Aaron Elzer, 32, of Coffs Harbour NSW

• Robert Rogers, 78, of Herberton Queensland

• Samson Tamaliunas, 12, of Western Australia

• Sheree Toope, 31, of Sydney

• Stuart Raymond Trott, 45, of Melbourne

• Susan Maree Cole, of Australia

• Tarli Sky Tonks, 14, of Tasmania

• Winona Langford, 17, of North Sydney

• Ziggy Viero, 7, of Australia

• Zoe Hosking, 15, of Adelaide

It comes after the first victim was officially named experienced tour guide Hayden Marshall-Inman, described as young and energetic with the "kindest heart".

His brother Mark Inman confirmed the news to friends and family on Facebook, saying Hayden passed away "doing the one thing he loved".

Friends remembered Mr Marshall-Inman as a "spectacular human" who was a generous, "lovely young man".

"He had the kindest heart, it was never about him. He definitely created a ripple effect of happiness to others, a very likeable guy," one woman wrote.

Former Whakatane mayor Tony Bonne also paid tribute to the young guide for White Island Tours, who he described as an "energetic man who's lost his life".

White Island Tours' website has been taken down and replaced with a message saying: "We are currently experiencing an emergency. For further information please contact us directly."

The Whakatane based company is one of the main staging points for trip to the volcano, known as Whakaari.

New Zealand police said five people have been confirmed dead and they believe there are no survivors left on the island following the eruption, leading to fears the number of casualties could be in the double digits.

Twenty three people made it off by boat. No victims have been officially named.

"No signs of life have been seen at any point," New Zealand police said on Monday evening.

"Police believe that anyone who could have been taken from the island alive was rescued at the time of the evacuation."

"Based on the information we have, we do not believe there are any survivors on the island.

"Police is working urgently to confirm the exact number of those who have died, further to the five confirmed deceased already."

Police said they will not be able to access the island overnight and will use a New Zealand Defence Force ship and drones to identify victims at first light.

"Both New Zealanders and overseas tourists are believed to involved, and a number were from the Ovation of the Seas cruise ship," police said.

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New Zealand Red Cross has activated its Family Links website and has received more than sixty posts from worried family members.

Forty-nine people have been listed as missing. Other nationalities listed include people from the UK, Guatemala, the Philippines, the US, Singapore, India, the Czech Republic and New Zealand.

So far, 16 people have confirmed they are alive.

Among the Australians registered missing by concerned family includes a seven-year-old boy and a 72-year-old man last seen aboard the Ovation of the Seas cruise.

"If you are worried about a friend or family member following this eruption, first contact them as you normally would," Red Cross advised on its website.

"Using your own channels can help to speed the process up and helps response agencies too. If you have lost contact with a family member or friend following the eruption, you can register them as missing."

The sister of a woman who worked as a tour guide to White Island and had gone to help with the rescue said her sister told her the event was "hectic and crazy".

"I'm guessing it would be just horrible, just sad and scary. She'd be pretty traumatised from the whole thing, just seeing people in that state," she told Stuff.

A Royal Caribbean spokesman said earlier: "We can confirm that a number of our guests were touring the island today. We do not have any additional details to share at this time.

"Ovation of the Seas will remain overnight until we learn more about the situation. We will offer all possible assistance to our guests and local authorities.

"Please keep all those affected in your prayers."