New Zealand has ordered about 1,290 square feet of human skin from the United States to help treat patients severely burned in Monday’s volcanic eruption on White Island, as emergency workers scramble to find at least nine people still missing amid concerns the volcano could erupt again.

There were at least 47 tourists on the island, which is also known by its Maori name, Whakaari, at the time of Monday’s eruption, including nine from the United States. Others were from New Zealand, China, Britain, Germany and Malaysia. At least six people were killed and many others injured.

Speaking to reporters in Auckland on Wednesday, Peter Watson, chief medical officer of the Counties Manukau District Health Board, said that 29 people, many with severe burns, are being treated in New Zealand’s hospitals. At least 22 are so badly burned they still need airway support, he said.

“The nature of the burns suffered is complicated by the gases and chemicals in the eruption,” Watson said. “This has necessitated more rapid treatment of these burns than is the case for thermal-only burns.”

Skin is the largest organ on the human body. Adults typically have around 20 square feet of skin, and some of the victims in New Zealand have burns on as much as 90 percent of their bodies.

Survivors are between the ages of 13 and 72. One Australian citizen would be transferred to Australia, Watson said, adding that other Australians would likely be transferred home in the coming days if they are approved for travel.

Surgeons have been working night and day to treat patients in what John Kenealy, clinical director of surgery and perioperative services at Middlemore Hospital in Auckland, told reporters was a record number of severe burn victims for New Zealand.

“This number of burns at one time is certainly unprecedented in New Zealand, and it’s unprecedented in most countries in the world,” Kenealy said. “These are, fortunately, rare events.”

Kenealy said he expects surgeons to spend around 500 hours total treating victims in the coming weeks and months.

Mark Law, a commercial helicopter pilot who assisted in the rescue of some survivors, told the Guardian this week that survivors were in terrible condition when he helped transfer them off the island.

“A lot of the people could not talk. It was pretty quiet. The only real words were things like, ‘help,’ ” he said. “They were covered in ash and dust. We were picking them up, and skin was coming off in our hands.”

Meanwhile, concerns the volcano is still active have hindered rescue teams’ ability to search for those who are still missing.

“I’ve spoken to many of those involved in the operation, and they are very, very eager to get back there; they want to bring people’s loved ones home,” New Zealand Prime Minister Jacinda Ardern told Reuters on Wednesday.

Graham Leonard, a senior volcanologist at one of New Zealand’s leading research institutes, GNS Science, told reporters in Wellington on Wednesday that there was a high risk the volcano would have erupted on Tuesday, Reuters reported.

“Today there is an even higher risk of an eruption,” he said. “And the parameters are worsening at the moment.”

Comments are not available on this story.