The accident happened in the Stoos ski resort late Thursday when a group of 10 people attending an event were coming down the mountain on a chairlift.
One of the chairs with four people on board hit a winch cable from a snow grooming machine and fell 10 metres (33 feet).
“A 33-year-old woman and a 40-year-old man suffered life-threatening injuries” and were evacuated by helicopter, local police for the central Schwyz canton said in a statement.
Two men aged 33 and 38 also suffered serious injuries.
Snow groomers are tracked vehicles used to smooth pistes for skiing. They use winch cables for safety when working on particularly steep slopes.