A group of hikers have stumbled across a rare sight of three eastern brown snakes romping in the grass at Tidbinbilla Nature Reserve in Canberra.

William Chancellor and friends were walking along the trail when they spotted the snakes.

"We got up further up the trail and we just saw these two snakes that were spinning around," he said.

"We weren't really sure what was happening, whether they were fighting or mating.