Fresno County officials confirmed the deaths but released no details.
Officials from the Naval Air Station in Lemoore said the F/A-18 went down about noon.
Authorities said emergency crews were at the scene but gave no other details.
F/A-18 Hornets are single-seat jets that are used by the military for combat operations and also in the Navy's Blue Angels Flight Demonstration Squadron, which performs aerial shows.
Lemoore is about 30 miles south of Fresno.
The Associated Press contributed to this report.