Authorities say three people were found dead and a fourth was taken to the hospital in Newport Beach.
Police received a phone call for medical aid on Monday morning from Balboa Island, Heather Rangel, a police spokesperson, said in an email.
Two women and a man were found dead. Another man was taken to the hospital, she said.
Rangel said there was no threat to the community. She did not immediately provide additional details.
Newport Beach is located about 40 miles (64 km) southeast of Los Angeles. Balboa Island is in Newport Bay.