The hospital said additional beds had been opened to relieve the pressure on the A&E department.
A spokesperson for Belfast Trust said the situation was brought under control just before midnight on Wednesday.
The RVH said anyone attending A&E could still expect to wait longer than normal.
Earlier on Wednesday evening, ambulances were diverted to the Ulster Hospital in Dundonald for several hours, but they are now returning to the RVH.
The hospital said some patients may still be transferred to other sites.
A spokesperson for the Belfast Trust said "everything that could be done, had being done".
She described it as a "very unusual situation".
The Royal Victoria Hospital (RVH) in Belfast has called in extra staff to deal with an unusually high volume of patients.