A device (10) for collecting and temporarily storing fluids (16) escaping from an underwater source (12, 64) and having lower density than surrounding water includes a collector (18) placed over the underwater source for collecting the escaping fluids, a riser tube (20) for transferring the collected fluids together towards the surface; and a buoyant buffer reservoir (22) maintained submerged under the surface and having an open-bottom chamber (30) for storage of the fluids. The riser tube has flow restrictors has flow restrictors comprising choke disks (58, 58′) arranged in its interior for restricting the flow of the fluids. The flow restrictors are arranged along the length of the riser tube. The buffer reservoir has arranged in its chamber a separator vessel (32) for separating gas from the fluids. The riser tube opens into the interior of the separator for discharging the fluids.