Survivors of last year's New Zealand volcano eruption are planning to sue cruise ship company Royal Caribbean for failing to warn of the risks involved in touring the area, lawyers said Monday.

There were 47 people, mainly Australian tourists, on White Island when it erupted on December 9 last year, killing 21 people.

Many were carried off with horrific injuries, including extensive external and internal burns from the explosion that sent steam, ash and gases hurtling from the caldera.

Lawyer Rita Yousef, from Sydney-based Stacks Goudkamp, said the firm was preparing to launch legal action against Royal Caribbean on behalf of survivors and families of the victims, many of whom were passengers on the cruise liner Ovation of the Seas.

Yousef said at least one Australian family and an unconfirmed number of others will sue for alleged negligence, breach of contract and violations of Australian consumer law.

New Zealand authorities on November 18 raised the Volcanic Alert Level for White Island from Level 1 to Level 2 -- the highest level before an explosion.

Yousef said there was "no indication at all that Royal Caribbean was paying attention to" the increased risk of the volcano erupting before a group of passengers joined a day-tour of the island.

"At the very least they should've informed their tour participants of the risk and let them decide if they wanted to take the risk," Yousef told AFP.

"We can go one step further and ask why were they even running these tours when there was such high risk? Why were they not cancelled?"

New Zealand has a "no-fault" public indemnity scheme that compensates both its citizens and tourists involved in accidents.

However, Yousef said the Australians caught up in the disaster had ongoing costs and losses that would likely far exceed those payments.

"We've got people who are having to deal with absolutely profound and unimaginable disability, the kinds of burns that a lot of medical professionals have never seen in their lives," she said.

Relatives have been grappling with "watching loved ones suffering in excruciating pain, and having to come to terms with -- if they survive -- what kind of quality of life they will have, will they ever be able to get back any sort of normality".

Yousef said it was hoped the legal action would also hold Royal Caribbean to account for its alleged failings.

New Zealand's government has launched an investigation into whether anyone was at fault in the tragedy but the probe is not expected to conclude before the end of this year.

Royal Caribbean did not immediately respond to a request for comment.