The 26-year-old man was surfing off Manresa State Beach around 1:30 p.m. when he was attacked by an unknown shark species, the California State Parks said in a statement.
The victim's name has not been released. Santa Cruz Sheriff's deputies notified the man's family.
The water one mile north and south of the attack will be closed for five days. Signs were posted warning beachgoers about the attack. The sign said the attack happened within 100 yards off shore.
"State Parks expresses its deepest sympathy to the family of the victim,'' the statement said.
The amount of surfing and swimming has been steady while local officials close the beach every day between 11 a.m. to 5 p.m. to deter a surge of visitors to the coastline during the coronavirus crisis.