"Everyone was watching football when unknown suspects approached the residence, snuck into the backyard and opened fire," Reed said.
He said three victims were killed on scene, identified as Asian males aged 20-35, and the fourth died in a hospital.
Fresno Police Lieutenant Bill Dooley said it was a "mass casualty incident", The Fresno Bee reported.
"Officers arrived on scene... What we found were several individuals deceased in the backyard." he said.
Meanwhile, a search operation is on to nab the accused.
This was at least the second fatal gun attack on Sunday in Fresno. A man in his 20s was shot dead earlier in the day at a home.
The police has not said if the two shooting incidents were related.