WATCH: Breaching humpback whale lands on top of kayakers

There’s whale-watching. And then there’s this U.K. couple’s close encounter with a humpback whale in Moss Landing, California.

Amazing video shows a fully grown humpback whale jump out of the water and land on top of a pair of kayakers in a tandem kayak.

Michael Sack, owner and captain of Sanctuary Cruises, was just a stone’s throw away when he and his passengers watched the enormous sea mammal leap.

“For them to jump out of water and land on somebody – that has never happened before as far I know. I would say it was just pure coincidence and the whale maybe didn’t know they were there,” Sack told Global News.

Tweet This Click to share quote on Twitter: "For them to jump out of water and land on somebody - that has never happened before as far I know. I would say it was just pure coincidence and the whale maybe didn't know they were there," Sack told Global News.

Sack’s vessel and about 20 kayakers had stopped to watch a group of whales playing and feeding on Saturday morning.

One of Sack’s passengers shot the whole thing. Sack posted the video on YouTube, where by Tuesday afternoon it had racked up more than 600,000 views.

It looked like the whale’s pectoral fin slapped the two kayakers, knocking them out of their boat and into the water.

They emerged uninjured – just a little shaken.

“They said it was one of the scariest things that ever happened to them,” Sack said. “They were in shock all day.”

Tweet This Click to share quote on Twitter: "They said it was one of the scariest things that ever happened to them," Sack said. "They were in shock all day."

Sack said on his blog the couple’s kayak appeared to have bent under the impact.

For the record, Sack doesn’t advise whale-watching in the kayak.

“It’s pretty crazy that it happened, but somehow they were OK,” he said. “It could have been a very serious matter. It could have been a lot worse.”