Photo: The Canadian Press

Rescuers land on White Island following eruption of the volcano.

A Canadian man says he is still "shaky" from the experience of witnessing the beginnings of a volcanic eruption in New Zealand.

The volcano off the New Zealand coast erupted Monday with a towering blast of ash and scalding steam as dozens of tourists were exploring its moon-like surface, killing five people and leaving eight others missing and feared dead, authorities said.

Sylvain Plasse, an actor from Toronto who is aboard a Royal Caribbean cruise ship, said he saw "huge smokes and plumes that went in billowing and then slowly morphing into different shapes and then being swept away" on an island across from him about 90 kilometres away.

Plasse was witnessing the beginnings of the eruption on White Island off the New Zealand coast.

At the time, he'd been taking a walk Monday afternoon on the foothills of Mount Maunganui in New Zealand. He'd climbed the steep slopes, got a bird's eye view of the beaches around the mountain and Tauranga, the city where his cruise ship is docked, and took lots of pictures of the "stunning" day, he said.

After the eruption, helicopter crews landed on White Island despite the danger and helped evacuate many survivors, some of them suffering critical burns. But officials said Tuesday they were still working with scientific experts to determine when it would be safe to return to the island to search for the missing.

Plasse described the experience as "just surreal."

"A day which was phenomenal was made even better (by seeing an eruption) until I got back to the ship and rumours started swirling that some crew and passengers were on tour of the volcano. And that joy turned to guilt and sadness. It was horrifying. It was totally heartbreaking."

He said the event is "still sinking in."

Global Affairs said in a statement the Government of Canada is closely monitoring the situation in New Zealand.

"At this time, there are no reports of any Canadian citizens being affected. Consular officials are in contact with local authorities to gather more information. We offer sincere condolences to the families and loved ones of the victims, and wish those injured a speedy recovery."

New Zealand Prime Minister Jacinda Ardern said aircraft have flown over the island repeatedly, and "no signs of life have been seen at any point."

Many of the 47 visitors on the island at the time of the eruption were Australian, and Ardern said New Zealanders and tourists from the United States, China, Britain and Malaysia were also affected.