  We study relations between quaternionic Riemannian manifolds admitting
different types of symmetries. We show that any hyperKahler manifold admitting
hyperKahler potential and triholomorphic action of S^1 can be constructed from
another hyperKahler manifold (of lower dimention) with an action of S^1 which
fixes one complex structure and rotates the other two and vice versa. We also
study corresponding quaternionic Kahler manifolds equipped with a quaternionic
Kahler action of the circle. In particular we show that any positive
quaternionic Kahler manifold with S^1 symmetry admits a Kahler metric on an
open everywhere dense subset.
