A couple from Horsham were threatened with a shotgun and a machete by raiders who forced their way into their home and demanded money
Sussex Police said up to six men men burst into the house in Longfield Road at 1915 GMT on Wednesday.
Officers said they struck the man in the face and threatened both victims before leaving within minutes with a few hundred pounds.
Det Insp Pierre Serra said it was not clear why their house was targeted.
He said: "This was a highly unusual attack, given the location and the reported number of offenders.
"We have a number of lines of inquiry and would like to hear from anyone who witnessed anything in the area around the time of the attack."
Both victims, who are in their late 50s, were taken to the East Surrey Hospital for treatment.
The man needed stitches to a cut to his cheek, a force spokesman said.