  We first prove some general results on pathwise uniqueness, comparison
property and existence of nonnegative strong solutions of stochastic equations
driven by white noises and Poisson random measures. The results are then used
to prove the strong existence of two classes of stochastic flows associated
with coalescents with multiple collisions, that is, generalized Fleming--Viot
flows and flows of continuous-state branching processes with immigration. One
of them unifies the different treatments of three kinds of flows in Bertoin and
Le Gall [Ann. Inst. H. Poincar\'{e} Probab. Statist. 41 (2005) 307--333]. Two
scaling limit theorems for the generalized Fleming--Viot flows are proved,
which lead to sub-critical branching immigration superprocesses. From those
theorems we derive easily a generalization of the limit theorem for finite
point motions of the flows in Bertoin and Le Gall [Illinois J. Math. 50 (2006)
147--181].
