A group of tourists kayaking off the coast of Kaikōura have had a shock after a seal suddenly slapped a party member with an octopus.

The group of official content creators for GoPro hit the water to capture footage with the new Hero 7 camera when they spotted the seal, 7News reports.

It was having a tussle with the octopus and New Zealander Kyle Mulinder told 7News they watched it for a while.

"We were just sitting out in the middle of the ocean and then this huge male seal appeared with an octopus and he was thrashing him about for ages," he told 7News.