A group of tourists was inadvertently introduced to Norwegian hunting practices during a whale-watching trip in the far north of the country.
Norway resumed commercial whaling in 1993
As they were admiring one of the animals, a Norwegian whaling boat came along and harpooned it.
Norway resumed commercial whaling in 1993 despite a worldwide ban, sparking condemnation from many nations.
Oslo says it has a large population of minke whales in its North Atlantic waters, not endangered by its hunting.
The tourists were travelling aboard a trawler which was headed for the Arctic Lofoten Islands.
"We were on our way out to the whale-watching area when we passed a whaling boat," the boat's skipper, Geir Maan, told the Associated Press news agency.
Whaling and tour boats usually maintained a distance between them, he said.
"This time, we got close, and right when they were passing, I realised they had a minke whale in firing range," he said.
The incident, which happened at the weekend, left the 80-odd tourists who witnessed it in shock.
"The blood flowed and it wasn't a pretty sight. This really wasn't what we came to see," Leontien Dieleman from the Netherlands told a Norwegian newspaper.
Later, the tour party passed a boat hauling a dead whale onto its deck.
This year, Norwegian whalers have been allowed to kill a total of 1,052 minke whales - 30% more than last year's quota - by parliamentary vote.
The International Whaling Commission banned commercial whaling in 1986, but Norway has rejected the ban.
The country's whaling association said the quota was acceptable as part of a "managed ecosystem".
Greenpeace described the quota increase as a "meaningless provocation of the international community".