The incident occurred shortly before 8:30 pm (0330 GMT Saturday) at a Spirit Halloween store at a shopping mall in Fairfield, about 47 miles (76 kilometers) northeast of San Francisco.

Fairfield Police Chief Dan Marshall told reporters one person was killed and six others were hospitalized with gunshot wounds. At least three were in critical condition, he added.

"There is still a very active crime scene and investigation going on right now," Marshall said late Friday, noting police had not yet identified the "suspect or suspects" responsible.

The shooting took place hours before the start of Halloween, which is celebrated in the United States on Saturday.

Marshall said no areas outside of the Solano Town Center mall were on lockdown.