IT WAS a cruise that Gavin and Lisa Dallow were excited to celebrate with her teenage daughter Zoe, 15, after a busy year and before another hectic summer.

And as their cruise set sail from Sydney Harbour last Wednesday night, Adelaide lawyer Mr Dallow, 53, sent a message to his twin sister, Meredith, at 7.07pm that revealed his joy.

Accompanying a panoramic picture of the waters and a Kiwi flag, it read simply: "Goodbye Australia. Next stop New Zealand."

Mr Dallow, a well-known Rotarian, and Zoe Hosking, 15, a Year 9 student at St Aloysius College, were still listed as missing on Tuesday night, amid grave fears for their safety after being caught up in the New Zealand volcano eruption.

His wife, a respected Santos engineer for the past 20 years, was fighting for life in a Hamilton hospital, with "severe" burns after being found by her Melbourne brother David Francis, on a mercy dash from Victoria.

The pair, from Nailsworth, in Adelaide's inner north, were among those still missing after the "active" volcano erupted on White Island at 2.11pm on Monday.

Their families were anxiously awaiting more news from diplomats as authorities scrambled to locate any survivors and identify the victims. The eruption, on the country's western coast, just southwest of Auckland, has killed at least six people with a further eight presumed dead.

Thirty one have been hospitalised - and some bodies are unlikely to be ever be recovered under the metres of ash and poisonous gas.

There were 24 Australians on the island at the time. NZ Police raised fears of no survivors on the island, following flyovers late on Monday.

Mr Dallow's family told The Advertiser how the pair had been looking forward to their trip, but expressed anger they had been allowed on to the island despite the dangers.

Meredith Dallow, a carer from Adelaide's northeast, described her brother as a strong family man, who loved to travel with his new wife and Zoe.

The trip was being used as a "break" before Mr Dallow would umpire at the Australian Open tennis championships in Melbourne, where he would be a linesman at his 12th tournament. Next year he planned to build his new legal practice after a decade at the Legal Services Commission, while he was helping Rotary with drawing up legal rules as it merged districts. "It wasn't their first cruise, they loved to travel. They were loving life and lived it to the fullest," the mother-of-three said. "They were always out doing something. We are all hoping for the best."

Her cousin, farmer Kym Loechel, 61, of Palmer, 74km east of Adelaide, said Mr Dallow was a careful man who would not have taken unnecessary risks: "I could not imagine in 100 years going himself, or taking people he cared about, into a dangerous situation or what was perceived to be."

Mr Dallow's anxious father, Brian, 85, speaking from his St Agnes home with wife Ruth, said they hoped for good news. "I'm wrecked. We had the phone with us all … night," he said.

But they thanked authorities, the operator of the Ovations of the Seas cruise as well as Phil Hoffman travel, who had booked the trip.

Mr Dallow met his wife on Flinders Street in the city - where they both worked - before they bonded over their shared Rotary passion.

He married "the love of his life" at Prospect Petanque Club in March 2017.

His family said he was heavily involved in community work as Rotary Club's assistant governor in SA while he loved sports, including following the Crows and Test cricket, which he watched last week with his father at Adelaide Oval.

He has been a tennis official since 2001 and had worked at the Davis Cup tie in February this year as a line umpire as well as various ATP Challenger-level events.

A spokeswoman said he "contributes regularly at local tournaments helping out at grassroots tennis events".

Colleagues and Zoe's classmates received counselling as friends awaited any news. St Aloysius Principal Paddy McEvoy told the school: "Our thoughts and prayers are with Zoe and her family. We know that you share our sadness at this time."