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Four people were fatally shot and six others wounded after at least two people opened fire at a family gathering in Fresno, Calif., on Sunday, then fled, the authorities said.

No suspects had been identified as of Monday morning, and the police said they were collecting statements from witnesses and running shell casings through a national database. The motive and number of assailants were unknown.

About 30 friends and family members were at the gathering at a home in Fresno when the gunfire began, Andy Hall, the chief of the Fresno Police Department, said at a news conference on Monday. The authorities received reports of the shooting shortly before 8 p.m. local time.

Chief Hall said the gunmen, who were armed with pistols, entered the property through an unlocked gate and began firing at people who were watching football in the yard.