It happened around 10:30 p.m. in the 11200 block of Town and Country Drive.
According to the Riverside Police Department, multiple calls began coming in about a shooting in which several people were injured.
When officers arrived, they learned four people had been shot and one had been stabbed.
Police said a sixth person, believed to be the shooting suspect, was also stabbed. The suspect, whose condition is unknown, has since been taken into custody.
Police said it appears the shooting may have stemmed from an altercation at the party, though further details weren't released.
The incident remains under investigation. Anyone with information is urged to contact police.