The house had been rented for the weekend and the owner told KCAL-TV in Los Angeles she found out around two dozen more guests than the six that were allowed had packed the oceanside home.
Between four and nine additional people suffered minor to moderate injuries when they fell on the rocks and sand, according to conflicting reports.
Shocking video posted on social media shows the moment the balcony gave way.
As many as 15 people were on the balcony when it collapsed and the victims fell between 10 and 15 feet before hitting the ground, an L.A. County Fire Department spokesman said, according to KTLA-TV in Los Angeles.
The homeowner said she was on the phone with the renters for hours trying to get the crowd to leave after her neighbors told her about the gathering, according to KCAL.
She said the balcony collapsed soon after she hung up -- it happened at around 5:30 p.m. PT.
The house has been declared uninhabitable by the fire department, KCAL reported.